The goals of this chapter are twofold. The first is to review the evidence on young children’s underlying capacity for dual language development. Understanding young children’s capacity for dual language learning is critical for having evidence-based expectations that shape parents’ and other caregivers’ decisions about whether and how to raise children bilingually. These findings can also inform families, educators, education administrators, health professionals, and policy makers about the most advantageous learning environments for dual language learners (DLLs)1 that will enhance their opportunities to learn the language (English) that is essential for their educational success in the United States. Multiple sources of evidence are relevant to this issue. This evidence includes studies with international samples outside of the United States and samples that varied widely in socioeconomic status, and studies with experimental, quasi-experimental, and correlational designs. In most of these studies, the children began learning their two languages from birth or before the age of 3. Although the samples from these studies may not be representative of the U.S. population of DLLs, they make a strong case for the human potential to learn more than one language and offer a picture of what is possible for DLLs in the United States.
The second goal of this chapter is to examine the factors that may influence the full expression of this capacity among DLLs in the United States.
1 As indicated in Chapter 1 (see Box 1-1), the term “dual language learner (DLL)” is used in this report to refer to children birth to age 5 in their homes, communities, or early care and education (ECE) programs.
Not all DLLs in the United States realize the potential of becoming fully proficient in English and their home language, as indicated by the striking variation among children in their trajectories and ultimate levels of achievement in their first (L1) and second (L2) languages. Thus, the second part of the chapter identifies the factors that help explain individual differences in the development of children’s language competencies. Three general sources of evidence were brought to bear on this issue. First were studies focused on the factors that benefit the learning of both L1 and L2. Second were correlational studies of children who began to learn a second language at different ages (specifically, before age 3 or after age 5). Most of these studies involved children who spoke a language other than English at home and began to learn English when they entered preschool or child care centers. A third source of evidence was experimental studies of monolingual children (mainly English speakers) learning a foreign language. Five broad categories of explanatory factors emerged from this literature: (1) timing of second language learning; (2) development of the home language; (3) the quantity and quality of language input; (4) cross-linguistic influences of L1 on L2 learning; and (5) broader sociocultural influences (beyond the quantity and quality of language experienced by children), including family socioeconomic status, school, and community contexts, that affect children’s opportunities to learn English and maintain their L1 and cultural heritage.
This section reviews research on children’s underlying capacity for dual language development from birth to 5 years of age. It begins with a review of research that has examined early stages in the development of critical components of dual language development: (1) language discrimination and speech perception; (2) early word learning, encompassing phonotactics (sounds), word segmentation and recognition, and associative word learning; (3) early vocabulary development; and (4) morphosyntactic2 development. Examining infants’ and toddlers’ language development during their early formative years gives insights into their capacity for learning language at the very outset. The section then illustrates DLLs’ capacity for adaptation and flexibility in response to the challenges of dual language learning
2 Morphosyntax, also referred to as grammar, describes how words are combined to make larger units such as phrases and sentences (e.g., the order in which subjects, verbs, and objects should appear in order to be correct in a language). It also describes how words are formed in a language (e.g., how nouns are pluralized, how verbs indicate past or present tense). Taken together, rules of morphology and syntax describe what is a well-formed sentence. Morphosyntactic rules are different for different languages. Morphosyntactic development refers to children’s and adults’ acquisition of the morphosyntactic rules or constraints that operate on the languages they are learning.
by reviewing research on communicative and cognitive aspects of their development.
Language Discrimination and Speech Perception
DLLs’ ability to discriminate among languages early in development is an important foundation for building two, or more, linguistic systems (Bosch and Sebastián-Gallés, 1997; see also Sebastián-Gallés, 2010, for a review of these studies). Language discrimination abilities allow the learner to separate different languages and connect the structural and functional properties of each (such as its sounds, words, and grammatical constraints). In addition, the ability to process speech sounds at 7 months of age correlates with the size of children’s vocabulary during the second year of life in both monolinguals (Kuhl, 2009; Tsao et al., 2004) and DLLs (Silvén et al., 2014). Thus, it is important to understand these early building blocks of dual language learning as precursors of subsequent and more complex aspects of language development.
Studies have shown that DLL infants have the language discrimination abilities they need to differentiate between the two languages they hear in their environments. When given the choice to listen to English or Tagalog, for example, neonates (ages 0 to 5 days) who had been exposed only to English listened to English more than Tagalog (Byers-Heinlein et al., 2010) because English was familiar to them and therefore preferred. In contrast, infants who had been exposed to both English and Tagalog during pregnancy and since birth could discriminate between the two languages and listened to both equally, indicating that both were familiar to them. Early discrimination abilities have likewise been documented in infants learning a different language combination—Spanish and Catalan—two languages that are much more similar to one another than English and Tagalog (Bosch and Sebastián-Gallés, 2001).
Other studies have shown that DLL infants may have enhanced language discrimination abilities. Monolinguals are unable to discriminate between languages that are rhythmically similar (e.g., Dutch and British English or Spanish and Italian) before 5 months of age (Bosch and Sebastián-Gallés, 2000; Nazzi et al., 2000), whereas bilingual infants have been found to distinguish between rhythmically similar languages (such as Spanish or Catalan) at 4.5 months of age (Bosch and Sebastián-Gallés, 1997). Rhythmic differences are a useful starting point for identifying other properties of the languages being heard. DLLs, for instance, use the rhythmic properties of their two languages to begin building the vocabularies and grammars of those languages (Gervain and Werker, 2013a). To take an example, languages differ in basic word order. The two most common word orders are subject-verb-object, in which the verb precedes the object (the cat
chased the dog) and subject-object-verb, in which the object precedes the verb (the cat the dog chased). Word order and prosody or rhythm are correlated, and infants can use the cues of prosodic prominence to figure out word order in their developing languages. One study found that infants 7 months of age who were learning two languages with different word orders could exploit the prosodic differences in the two languages to segment noun phrases from continuous speech (Gervain and Werker, 2013a). These findings attest to the capacity of DLLs to use cues in language input to abstract higher-order features of language.
Infants also are adept at learning the specific sounds and sound sequences of language. Languages differ in the sounds used to construct words and convey meaning. Sounds that carry meaning in individual words, such as /l/and /r/in English, are called phonemes; using /l/instead of /r/changes the meaning of the word (e.g., lot and rot). These sounds are not phonemic in Japanese, so that interchanging /l/and/r/when speaking Japanese does not change the meaning of individual words. Extensive research has shown that infants begin life with the ability to discriminate many consonant and vowel sounds found in the world’s languages, regardless of their experience with specific languages (e.g., Trehub, 1976; Werker and Tees, 1984). These findings point to an important capacity for DLLs to discriminate many of the sound segments they need to construct two languages.
Experience does matter, however. Researchers have found that infants’ ability to discriminate speech sounds becomes language-specific during the second half of the first year of life (at about 6-9 months of age) (Gervain and Werker, 2013b; Kuhl et al., 2006). They continue to discriminate acoustic contrasts that are phonemic in their native language after this age, but gradually begin to lose the ability to discriminate contrasts that are not phonemic in that language. Monolingual infants perceive language-specific vowel contrasts by 6-8 months of age (Bosch and Sebastián-Gallés, 2003; Kuhl et al., 1992) and consonant contrasts somewhat later, by 10-12 months of age (Werker and Tees, 1984). DLLs go through a similar reorganization in speech perception at roughly the same ages (Albareda-Castellot et al., 2011; Burns et al., 2007; Sundara et al., 2008; Vihman et al., 2007).
Not all phonemic contrasts are equally easy to learn, and as a result, DLL infants whose languages contain contrasts that are difficult to discriminate may take longer than monolinguals to discriminate some of the contrasts in the languages they are learning. Sebastián-Gallés and Bosch (2002) explored the ability of monolingual and bilingual infant learners of Spanish and Catalan with respect to the Catalan-specific contrast /e-ε/, as in English “late” and “let” (Sebastián-Gallés and Bosch, 2002). This phonetic contrast is not phonemic in Spanish, and adult Spanish speakers thus have difficulty perceiving it (Sebastián-Gallés and Bosch, 2002). The authors found that infants in all three language groups (monolingual in each lan-
guage and bilingual) could distinguish the Catalan contrast at 4 months, whereas only the monolingual Catalan learners could discriminate the contrast at 8 months. The bilingual infants could discriminate this contrast a bit later, at 12 months of age. The researchers suggest as an explanation for their results that the Spanish-Catalan bilingual infants may have treated the /e- / contrast in Catalan as a single category because it is a single phonemic category in Spanish. As a result, they required more time and possibly more input to disentangle the subtle distributional properties of these sounds in Catalan and Spanish. The important point here is that the perceptual performance of DLL infants may differ from that of monolinguals because of competing phonetic properties of their two languages, which can be quite subtle at times and may thus require more exposure to learn.
At the same time, neuroimaging evidence indicates that the strategies used by DLLs may differ in kind or degree from those used by their monolingual counterparts insofar as bilingual and monolingual toddlers show different patterns of brain activity during performance of the same task (Conboy and Mills, 2006; Ferjan Ramirez et al., 2016; Shafer et al., 2011). Conboy and Mills (2006) used event-related potential (ERP) techniques to study the neural responses of bilingual Spanish-English toddlers ages 19-22 months during a task in which they listened to known and unknown words (Conboy and Mills, 2006). The DLL and monolingual toddlers exhibited different patterns of activation, with the DLLs showing relatively greater activation in the right hemisphere, as well as ERP effects that were distributed more broadly across the brain. These findings illustrate that experience with language shapes “the organization of brain activity for language processing” (Conboy, 2013, p. 19), which in turn may alter the way in which the brain processes and acquires language in future stages of development.
The developments reviewed to this point provide infants with fundamental building blocks for continued language development. The next sections review what research reveals about how they use those building blocks to construct larger and more complex units of language—the sound combinations, words, and grammars of their languages.
Early Word Learning
Three different but interrelated lines of research are relevant to early word learning in DLL infants: phonotactics, word segmentation and recognition, and associative word learning. Research in these domains is relatively limited, and thus the evidence is still emerging. Nevertheless, a coherent understanding of this stage of dual language learning is already beginning to emerge, one that emphasizes processes common to all language learners and those reflecting variability linked to unique features of dual language learning.
Languages differ not only in their phonemic inventories, as noted earlier, but also in the sequences of phonemes they use to construct words. This property is referred to as phonotactics—the permissible sequences of sounds in a given language. Infants learn the sound sequences of their languages from exposure to those languages over time. Learning the phonotactic regularities of two languages early in development does not appear to be more challenging than learning those of only one. Sebastián-Gallés and Bosch (2002), for example, found that 10-month-old monolingual Catalan infants preferred listening to Catalan-sounding pseudowords that used Catalan phonotactics over Spanish words that did not use Catalan phonotactics. The Catalan-dominant bilinguals also preferred listening to the Catalan pseudowords, as expected. The Spanish-dominant bilinguals exhibited a mild preference for words that conformed to Catalan phonotactics over words that violated Spanish phonotactic constraints. And the Spanish monolinguals exhibited no preference, as would be expected since the contrast was specific to Catalan. These findings indicate that dual language learning does not compromise infants’ ability to learn the phonotactic constraints of a language or to recognize words (Vihman et al., 2007), and that the amount of language exposure or relative language proficiency can influence DLLs’ development of phonotactic knowledge (see also Garcia-Sierra et al., 2011).
Word Segmentation and Recognition
A number of researchers have examined DLL infants’ ability to extract words from continuous speech. Doing so is difficult for all infants since there are no clear acoustic cues that signal the beginnings and endings of words when they occur in continuous speech, so infants must know the phonotactic regularities of their language(s). In a study of DLL infants learning Spanish and Catalan and monolingual infants learning Spanish or Catalan, infants preferred familiar to new words, indicating that they perceived differences between the two (Bosch et al., 2013). Both dual and monolingual language groups exhibited more advanced segmentation abilities at 8 months (namely, a novelty effect) than at 6 months (a familiarity effect). French-English dual language 8-month-old infants also were able to segment familiar words from both languages in continuous speech (Polka and Sundara, 2003).
At the same time, evidence suggests that it takes time for children to acquire stable detailed representations of the sounds that make up words and, in some instances, DLLs may take longer to do so than monolingual learners. Ramon-Casas and colleagues (2009) examined whether 18-month-
old bilingual Catalan-Spanish, monolingual Spanish, and monolingual Catalan children could recognize mispronounced words. Critically, the mispronounced words were created by exchanging the Catalan-specific /I-ε/contrast in some words, a contrast that does not exist in Spanish, thereby producing target words such as fish and fesh that should sound like two different words in Catalan but like the same word in Spanish. They found that the Catalan monolinguals more often recognized the correctly pronounced target word (fish), suggesting that they perceived the mispronunciation. In contrast, neither the monolingual Spanish children nor the Spanish-Catalan bilinguals displayed differential recognition of the correctly and incorrectly pronounced word. These results suggest that bilinguals may take longer than monolinguals to learn certain phonological properties of one of their two languages because the task is more complex than that faced by monolingual children. It may be that DLLs take longer than monolinguals to establish stable phonological representations of word forms because they are exposed to less input in each language or to non-native input in one or both of their languages.
Associative Word Learning
Further insights into infants’ early word-learning capacities come from studies that have examined their ability to associate novel words with referents or objects. To examine young learners’ associative word learning ability, Byers-Heinlein and colleagues (2013) examined 12- and 14-month old DLLs and monolingual infants on a word-learning task involving new words that differed phonetically in several ways (e.g., lif and neem differ in all three of their phonemes). The monolingual participants were from English-speaking families, while the DLL participants had been exposed to English and another language from birth. The children were first exposed to novel word-object pairings several times—for example, the word lif was presented with a novel object shaped like a molecule, and the word neem was presented with a novel object shaped like a crown. During the test phase, following the familiarization phase, the children were presented with either the same word-object pairing or a switched pair in which a familiar word was shown with another object. Infants’ differential looking times during the switched and nonswitched trials is considered evidence that they have learned the new word-object pair, and presumably the meaning of the new word. The findings of this study suggest that neither the monolingual nor DLL infants detected a violation of the previous word-object pairings at 12 months of age, but both groups succeeded, with no difference in performance between them, at 14 months of age.
Learning to associate objects with novel words comprised of minimal pairs—words that differ by only one phoneme, such as the pair /bih/ and
/dih/, is more difficult. Fennel and colleagues (2007) found that infants who were learning one language could learn associations between new words comprised of minimal pairs and their referents at 17 months of age, whereas DLLs were able to learn these associations only at 20 months of age, suggesting that they needed more time to succeed at this difficult task. Further research by Fennell and Byers-Heinlein (2014), as well as Mattock and colleagues (2010), revealed that DLLs could succeed at this demanding task at the earlier age (17 months) when the sounds were produced by bilingual speakers. In contrast, 17-month-old monolingual children were unable to learn novel minimal pairs of words produced by bilingual speakers. These findings illustrate that the experimental conditions for studying DLLs may not always match the conditions in which the children have actually learned and used language, and that the language environment experienced by DLLs is not simply the sum of two monolingual environments. There may be qualitative differences between the input to which bilinguals are exposed in each language and the input from monolingual speakers of the corresponding languages.
There is evidence that DLL infants demonstrate adaptability when learning two languages; for example, they are more likely than their monolingual counterparts to accept mispronounced words since they may be spoken by non-native speakers, and they are able to use visual information about mouth shape to discriminate languages for an extended period in development (Werker, 2012). Additional evidence on the adaptable strategies used by DLLs to learn language comes from research examining the use of the “mutual exclusivity” constraint. Mutual exclusivity is thought to help monolingual children in word learning such that when they hear a new word, they tend to associate it with a novel object rather than an object for which they already have a label. This has been shown experimentally in 17-month-old monolingual infants and young children (e.g., Halberda, 2003; Markman, 1989). Yet while mutual exclusivity may be a useful heuristic for learning one language, where objects are often associated with only one common label, this is not the case for children learning more than one language, where objects usually have more than one label. A number of studies of DLLs have shown that they are less likely than their monolingual counterparts to apply the mutual exclusivity constraint in experimental situations (e.g., Bosch and Ramon-Casas, 2014; Byers-Heinlein and Werker, 2009; Houston-Price et al., 2010). Analyses of DLLs’ natural language use also indicate that they often have labels in both languages for the same objects (Pearson et al., 1993), in violation of the mutual exclusivity constraint. That children learning more than one language do not honor the mutual exclusivity constraint also shows how their pattern of development is different from that of monolingual learners.
Early Vocabulary Development
When simultaneous DLLs’ scores on standardized vocabulary measures and/or parent report measures are examined separately, they often are lower than those of monolingual children learning only one of the languages, even after controlling for socioeconomic factors (Hoff et al., 2012, discussed in greater detail later). However, they are at the same level as or higher than the scores of monolinguals when both languages are considered together. On their own, these results give the impression that DLLs have reduced capacity for vocabulary learning. However, assessing one language of DLLs does not provide a complete picture of their vocabulary knowledge. In a landmark study of Spanish-English bilingual children in the United States (8-30 months of age; average socioeconomic status 2.2 on a 5-point scale, with 1 being highest), Pearson and colleagues (1993) found no differences between DLL and monolingual children when the DLLs were given credit for knowing words in both languages, or what is referred to as conceptual vocabulary.3Hoff and colleagues (2012) also examined the vocabulary and grammatical development of Spanish-English bilingual infants and toddlers in the United States. Their study included 47 Spanish-English bilingual children and 56 monolingual English-speaking children from high socioeconomic environments. Overall, they found that the monolingual children scored higher than the bilingual children on both English vocabulary and grammar indices from the MacArthur Communication Development Index when each language was considered separately. In contrast to the single-language results, however, there were no significant differences between the two groups of children when total vocabulary in English and Spanish was calculated and when combinatorial speech in both languages was assessed. These results have been replicated by researchers around the world working with different language combinations and children at different socioeconomic levels (see De Houwer, 2009, for a review).
Evidence that DLLs exhibit the same language-specific and appropriate grammatical knowledge as monolinguals at similar ages would provide additional evidence that DLLs have the capacity to acquire two languages without jeopardizing the development of either. This section reviews studies on the grammatical development of DLLs from approximately 2 to 5 years of age. The reviewed research addresses the following three interrelated questions: (1) Do DLLs acquire separate grammatical systems? (2) Do the
3 Scoring for conceptual vocabulary gives credit for each word that refers to a different concept regardless of the language of that word; words that refer to the same concept are counted only once.
grammars of DLLs exhibit the same developmental patterns as those of children learning only one language? and (3) Is the rate of grammatical development affected by the acquisition of two languages?
Do DLLs Acquire Separate Grammatical Systems?
An early and predominant issue in research on the grammatical development of DLLs is whether they acquire differentiated grammatical systems and if so, how early in development this is evident (Genesee, 1989). There is, in fact, consensus among researchers that DLLs acquire separate grammatical systems for the most part and under most circumstances (see De Houwer [2009, App. G, p. 350], for a synopsis of studies that support this view) and that this is evident from the earliest stages of grammatical development.
One source of evidence that led researchers to think initially that DLLs were “mixing up” their languages is the phenomenon known as code switching (sometimes called code mixing).4 When DLLs code switch (that is, use elements from their two languages in the same utterances), they usually do so in ways that respect the grammatical constraints of each language (see Genesee, 2002, for a review). For example, if a developing Spanish-English DLL child uses words from English when speaking with a Spanish-speaking person, the English words will be inserted into a Spanish grammatical phrase so that the word order of Spanish is respected. DLLs also usually avoid affixing grammatical morphemes (the smallest unit of meaning in a language) from one language to words in the other language. Such grammatically constrained code switching is observed as soon as DLLs begin combining words into simple two-word utterances. That DLL children code switch in this way attests to their having acquired the underlying grammatical constraints of the two languages.
Further evidence that DLLs have separate grammars is that during the two-word and multiword stage of their language development, they produce many more single-language than mixed-language utterances (De Houwer, 2009; Genesee et al., 1995; Schelletter et al., 2001). If DLLs were, in fact, acquiring undifferentiated grammatical systems, the majority of their utterances would be expected to violate the constraints of one or both languages, as predicted by Volterra and Taeschner (1978), because they would not have reached the stage in development when differentiation of the two grammars had occurred. The neurolinguistic evidence is also consistent with these conclusions (Kovelman et al., 2008b).
4 Researchers who study language development and use in bilingual children tend to use the term code mixing.
Do the Grammars of DLLs Exhibit the Same Developmental Patterns as Those of Children Learning Only One Language?
Studies of the grammatical development of DLLs indicate that for the most part, they acquire language-specific and appropriate patterns in each language and that these are the same patterns exhibited by monolinguals, other things being equal (see De Houwer  for a review). With respect to general patterns of morphosyntactic development, DLLs, like young monolingual learners, go through one-word, two-word, and then multiword stages of development, and they do so at approximately the same ages. It has been well established that monolingual children begin to produce two-word combinations after they have acquired about 200 words (e.g., see Bloom, 1993; Hoff et al., 2012; Marchman and Bates, 1994); the same link between vocabulary size and early word combinations is seen in DLLs (David and Li, 2004; Junker and Stockman, 2002; Patterson, 1998). There is also a correlation between vocabulary size and overall complexity of utterances produced by both DLL and monolingual children (Marchman et al., 2004).
With respect to specific aspects of grammar, it has been found that, at a given age or mean length of utterance (MLU),5 DLL and monolingual children learning the same languages usually demonstrate knowledge of the same grammatical structures and constraints (see De Houwer  for a review of relevant studies). Spanish-English DLLs, for example, exhibit language-specific and appropriate use of predicates and closed-class words6 in both languages (Conboy and Thal, 2006). Spanish-English DLLs and same-age typically developing monolingual English learners in the United States do not differ on finite verb accuracy and use of obligatory overt subjects in English (mean age 5 years, 7 months; range 4 years, 5 months to 6 years, 5 months) (Gutiérrez-Clellen et al., 2008). In short, DLLs and young monolinguals show the same general developmental patterns and relationships.
Is the Rate of Grammatical Development Affected by the Acquisition of Two Languages?
When milestones in grammatical development are examined and when adequate amounts of exposure to each language are available to the learner,
5 MLU is the average number of words or morphemes in a stretch of language use, often 100 words. It is generally interpreted as an indicator of level of grammatical development in young learners.
6 Function or closed-class words are words such as prepositions, conjunctions, articles, and auxiliaries; these words play an important role in establishing relationships between words in a sentence, but they lack referential meaning.
there is no evidence that DLLs are likely to fall behind norms established for monolingual learners. This finding holds for indices such as MLU (Paradis and Genesee, 1996); emergence of two-word combinations (around 2 years of age), noted previously; production of short sentences with some inflectional morphemes (around 30-36 months of age); and production of complex utterances/sentences (around 48 months of age) (see De Houwer [2009, p. 37] for a summary of language development milestones from birth to age 5). The robust similarity in the emergence of these milestones in monolingual children and DLLs learning different language combinations implies a universal, underlying human capacity to learn two languages as easily as one.
Communicative and Cognitive Capacity of Dual Language Learners
Additional evidence for DLLs’ capacity for learning more than one language early in development comes from studies that have examined their communicative competence using two languages and their cognitive flexibility.
DLLs demonstrate impressive capacity to manage their two languages when communicating with others. Systematic examination of this issue has demonstrated that even very young DLLs use their two languages in communicatively appropriate and competent ways—they differentiate use of each language according to the language known or preferred by the people to whom they are speaking. Research on this question has examined DLLs in early stages of verbal development when they are producing mainly one- and two-word utterances, because it is during this stage of development that communication might be expected to be most challenging. Genesee and colleagues (1995) studied 2-year-old children from varied socioeconomic backgrounds who were acquiring French and English simultaneously from their parents, who used the one parent/one language pattern with their children. They found that the children were able to use the appropriate language with each parent. In a follow-up study, English-French DLLs (average age of 2 years, 2 months) were able to use their languages appropriately with strangers, indicating that DLLs’ ability to use their two languages differentially and appropriately did not depend on prior experiences with particular speakers and, moreover, was within their capacity from the earliest stages of development (Genesee et al., 1996).
DLLs also demonstrate impressive control over the use of their languages, even though both are still developing (Comeau et al., 2003, 2010; see Petitto et al., 2001, for similar evidence from children learning oral and
sign languages simultaneously). In a quasi-experimental study, for example, 2- and 3-year-old French-English bilingual children who used the “wrong language” with a monolingual interlocutor/stranger whom they had never met before switched languages when the interlocutors indicated that they did not understand what the child had said (Comeau et al., 2007). Of particular importance, the children switched languages even when their interlocutors used a very general prompt, such as “What?,” that did not indicate the source of the breakdown, indicating that managing their two languages was not a challenge. Taken together, this evidence is difficult to reconcile with concerns that early dual language learning can engender confusion.
Recent evidence points to certain cognitive advantages among children (and adults) who are competent in two languages (see Baum and Titone  for an overview, including opposing views, on this issue). This section briefly reviews these advantages.
Executive functioning refers to a set of cognitive abilities that allows individuals to plan, control their attention, regulate their behavior, and think flexibly (Miyake et al., 2000). It has been argued that learning and using two languages enhances executive functioning because bilinguals engage the areas of the brain (the prefrontal cortex, the inferior parietal lobule, and the basal ganglia) that are involved in reducing potential interference between their languages and ensuring the activation of the appropriate language depending upon the situation. Thus, bilinguals often exhibit a broad set of advantages that are related to the ability to control their focus of attention. These advantages include the ability to switch their focus of attention, reason about others’ mental states, and reflect on the structure of language itself (Bialystok, 1999; Bialystok and Senman, 2004; Bialystok and Shapero, 2005; Bialystok et al., 2003, 2008; Carlson and Meltzoff, 2008; Costa et al., 2008; Friesen and Bialystok, 2012; Kapa and Colombo, 2013; Martin-Rhee and Bialystok, 2008; see Gordon, 2016, for a recent review) a process known as metalinguistic awareness.
A bilingual advantage in switching attention has been observed in DLL infants as young as 7 months of age who are better able than monolinguals to reorient their attention to a new location to obtain a reward (Kovács and Mehler, 2009) and 8-month-olds who, unlike their monolingual counterparts, can visually discriminate when a speaker switches from French to English (Sebastián-Gallés et al., 2012). Such advantages also have been observed in DLLs (English-Welsh) who begin to learn a second language as late as 4-6 years of age (Kalashnikova and Mattock, 2014). Bilinguals may have advantages as well in spatial and verbal working memory—other components of executive functioning—even after controlling statistically for
Although evidence suggests that bilinguals may exhibit an advantage in short-term memory (Morales et al., 2013), this advantage appears to be unstable and has been attributed to vocabulary size rather than bilingualism per se (e.g., Engel de Abreu et al., 2011). Moreover, advantages in visual attention and visual perception have not always been observed (Schonberg et al., 2014). In addition, a number of researchers have openly questioned whether monolinguals and bilinguals differ in their behavioral performance on cognitive control tasks (Abutalebi et al., 2012; de Bruin et al., 2015; Duñabeitia and Carreiras, 2015; Dunabeitia et al., 2014; Hernandez and Kohnert, 2015; Hilchey and Klein, 2011; Paap and Greenberg, 2013; Paap et al., 2014). In a recent meta-analysis of the cognitive advantages of bilingualism, de Bruin and colleagues (2015) suggest a bias toward publishing studies with results that support the bilingual advantage. Some evidence also suggests that cognitive control may be heritable (Friedman et al., 2008; Lee et al., 2012) and that it is related to socioeconomic status (Noble et al., 2005) and parenting style (Bernier et al., 2010), evidence that argues against the importance of bilingualism per se.
In response to suggestions of bias, researchers have sought to identify the circumstances under which bilingual advantages are observed (Baum and Titone, 2014). These advantages are observed most commonly among bilinguals who became highly proficient in both of their languages at early ages (Gordon, 2016). That a cognitive advantage may not be reported in all studies under all conditions is not surprising since the kinds of performance and reasoning examined—problem solving, planning, and divergent thinking—are likely to be influenced by multiple factors, of which bilingualism is only one. Thus, different results may be found under subtly different testing conditions and for children of different backgrounds. Moreover, it appears likely that the relationship between bilingual competence and cognitive ability is one not simply of positive or negative but of varied and complex effects. In addition to advantages, for example, there are what might be considered disadvantages associated with bilingualism. Specifically, relative to their monolingual counterparts, adult bilinguals often show slower access for words presented in isolation (Pelham and Abrams, 2014) and in phrases (Sadat et al., 2012) and lower levels of oral fluency (Portocarrero et al., 2007).
In summary, there is no evidence to indicate that use of two languages in the home during the birth to 5 period poses a risk to children’s development of one or both languages. Given adequate exposure to two languages, young children can acquire full competence in both. Nonetheless, DLLs and monolinguals do not exhibit exactly the same developmental trajectories or exactly the same skills in each language. In addition to the factors dis-
cussed in the next section on influences, differences can arise because DLLs face complexities that monolingual learners do not; specifically, they are learning two or more languages with different phonological, lexical, and morphosyntactic properties that may be ambiguous or incompatible with one another. These differences are perfectly normal and typical for DLLs, even though they result in these children’s looking and sounding different from monolingual children of the same age. Finally, current evidence suggests that dual language learning does not appear to pose communicative or cognitive challenges, and to the contrary, it may under some conditions enhance the child’s cognitive resources.
Children’s impressive capacity to acquire at least two languages is seen across multiple components of language, with certain sensitivities arising before birth. However, capacity does not imply competence, and there are striking individual differences among children in their trajectories and ultimate levels of achievement in their two languages. What factors explain individual differences in the development of DLLs’ language competencies? This section reviews evidence that points to the following categories of influence: (1) timing of second language learning; (2) development of the home language (L1); (3) the quantity and quality of language input; (4) cross-linguistic influences of L1 on L2 learning; and (5) broad sociocultural influences, including family, socioeconomic status, school, and community contexts, that affect children’s opportunities to learn English and maintain their L1 and cultural heritage. Understanding the influence of these factors on development is important for understanding DLLs and for optimizing their language learning.
Timing of Second Language Learning
Both developmentalists and the public strongly believe that there is a “critical” period for language learning, and indeed the evidence is strong that such a period exists in the case of first language learning (Lenneberg, 1967; Werker and Hensch, 2015). However, the evidence for a critical period in the case of second language learning is mixed and controversial. The literature on dual language learning uses the phrase age of acquisition (AoA) to refer to the learner’s age when beginning to acquire an L2 (Hernandez and Li, 2007). An AoA effect is seen for L2 learning, with early exposure being consistently associated with relatively higher levels of L2 attainment relative to later exposure (Flege et al., 1995, 1999; Mackay and Flege, 2004; Munro et al., 1996). It should be noted, however, that there are individual cases in which later exposure can result in native-like
proficiency on tests of English grammar (Birdsong, 1992). The facilitative effects of early exposure might be explained by the trajectory of early brain development and align with findings discussed earlier that young children have the neural capacity to learn two or more languages from birth (see Box 4-1 for further discussion). There is also evidence that age of exposure to L2 affects processing of certain components of language (phonology, morphology, and syntax) more than others (such as semantics and vocabulary) (Johnson and Newport, 1989; Mitchell et al., 2013; Weber-Fox and Neville, 1996). There continues to be debate about whether and when the capacity to fully learn an L2 begins to decline, with researchers acknowledging that there is no strict cut-off point after which it is no longer possible to acquire an L2. And, as will be reviewed in a subsequent section, DLLs’ L2 proficiency (like proficiency in L1) depends to a large degree on the quantity and quality of language to which they are exposed.
Early Versus Late Exposure
Early exposure to L2 input is consistently associated with better language skills in L2 (e.g., Dupoux et al., 2010; Meisel, 2011; Ortiz-Mantilla et al., 2010). For example, children exposed to proficient speakers in L1 and L2 before 3 years of age (simultaneous bilinguals) outperformed children with an onset of L2 exposure later than age 3 (often referred to as sequential or successive bilinguals) in morphology and phonology in both languages (Weber-Fox and Neville, 1996, 2001). Similar studies have shown better performance in reading, phonological awareness, and overall competence in both languages (Kovelman et al., 2008a). These AoA effects are especially strong in areas of phonology, morphology, and syntax—domains of language that Hernandez and Li (2007) argue rely on sensorimotor processing. In phonology, for example, late L2 learners show clear accents, even after years of speaking the L2.
Additionally, and as noted earlier, children exposed to two languages simultaneously demonstrate the same developmental trajectory in each language as that seen in monolingual children, for the most part (De Houwer, 2009), provided they have adequate exposure to each (a topic covered later in this chapter). Similarities in language development between simultaneous DLLs and monolingual children have been found in the acquisition of vocabulary and grammar and in the relations between children’s vocabulary and grammatical development in each language, among other measures (Conboy and Thal, 2006; Marchman et al., 2004; Parra et al., 2011).
Neural Development and Age-of-Acquisition Effects
The benefits of early exposure to L2 for the language development of DLLs may be explained by developmental changes in the brain (see Box 4-2). When dual language learning occurs from birth to 3 years of age, the neurocognitive changes in the brain are the same or nearly so for both (or all) languages being learned. When children begin to acquire an L2 after approximately 3 years of age, however, some neural commitment to the language already learned has occurred, so the brain is not in the same state it was in earlier. In fact, magnetic resonance imaging (MRI) studies of cortical thickness show no differences in brain structure between simultaneous bilinguals (exposed to L2 before age 3) and monolinguals, whereas “late bilinguals” (those who acquired L2 after gaining proficiency in L1) had modified brain structures relative to the other two groups (Klein et al., 2014). Even a delay of 1 year may change the way the brain acquires language (Pierce et al., 2015). As a result, the processes, rates, and outcomes of learning are likely to be the same or highly similar for both languages when dual language learning occurs during infancy and toddlerhood—provided
learners experience adequate exposure to each language—in contrast to L2 exposure that occurs after 3 years of age (Pierce et al., 2015).
In particular, neural systems crucial for sensorimotor learning and coordination undergo rapid organization and reorganization early in life (Hernandez and Li, 2007) and may be responsible for declines in plasticity
that result in difficulty forming complex mappings later in life (Bates, 1999; Bates et al., 1997; Hensch, 2004; Pickett et al., 1998). Rates of synaptogenesis7 and pruning8 occur earlier in the sensory cortices that process speech sounds than in the “higher” brain networks involved in combining words into sentences. Early and rapid changes to sensorimotor systems may be important to language since the articulation of speech sounds is a sensorimotor process. A child’s developing skills in L1 and L2 pronunciation require precise control and temporal coordination of articulatory actions in the speech apparatus (tongue, lips, jaw, larynx, etc.) (Hernandez and Li, 2007).
Finally, simultaneous and successive bilinguals differ in neural circuitry between the left and right regions of the brain and among brain areas involved in language control (Berken et al., 2016). Specifically, earlier AoA for an L2 leads to stronger functional connectivity, which may allow simultaneous bilinguals to regulate the two competing language systems efficiently (Abutalebi and Green, 2007; Green, 1998; Stocco et al., 2014), thereby leading to more efficient language control networks. In contrast, late L2 onset means learning of language occurs after networks have been established, and the individual must rely on modifications of existing circuitry (Berken et al., 2016).
Children exposed to an L2 early in development also have more exposure to and practice using the language, which supports proficiency with the language. Testing of AoA and proficiency together for their associations with neural responses yields conflicting results as to which is the stronger predictor of brain activation patterns (Hernandez and Li, 2007; Rossi et al., 2006; Steinhauer et al., 2009). Proficient bilinguals, whether early or late learners, show strikingly similar neural responses for both L1 and L2 that differ from the neural responses of less proficient bilingual individuals (e.g., Abutalebi et al., 2001; Chee, 2006; Perani et al., 1998). Still, greater AoA effects are seen for syntactic than for semantic processing tasks (Hernandez et al., 2007a; Waldron and Hernandez, 2013; Wartenburger et al., 2003; Weber-Fox and Neville, 1996).
Development of the Home Language (L1)
To what extent does ability in L1 support or hinder the acquisition of L2? Some immigrant parents may fear that talking with their child in L1 will compromise the child’s ability to learn English and subsequently succeed in U.S. schools because the development of L1 will slow and perhaps even interfere with English acquisition. Teachers also express this concern.
7 Synapses are the connections between neurons (nerve cells). Synaptogenesis is the formation of these connections.
8 Pruning is the elimination of extra neurons or synapses.
To the contrary, however, growing evidence indicates that strong L1 literacy and vocabulary facilitate the development of skills in a second and even third language (Brisk and Harrington, 2007).
The importance of L1 skills for learning a new language is evident during the emergence of language, as indicated by experimental studies aimed at teaching a new language to toddlers. Koening and Woodward (2012), for example, examined monolingual English-speaking toddlers’ ability to learn words for objects in Dutch versus English. Toddlers with large English vocabularies successfully learned the words in Dutch, whereas those with low English vocabulary scores responded at chance levels. These findings suggest that having a large vocabulary in their native language supports toddlers’ ability to learn words in another language.
Cross-language associations have been documented for phonology (Kohnert et al., 2010) as well as semantic priming, in which hearing a word such as “table” leads to faster recognition of a related item such as “chair” (Singh, 2014). Priming effects for DLL toddlers also have been shown to exist for words that are phonologically similar across the two languages (Von Holzen and Mani, 2012).
Studies of deaf children learning American Sign Language (ASL) and English offer strongly compelling evidence that L1 development facilitates L2 development, illustrating the effect even across different modalities. Boudreault and Mayberry (2006) compared the L2 (English) proficiency of two groups of deaf children: (1) those who had begun to acquire ASL early and (2) those who had begun to acquire ASL later and had acquired no language earlier in development. Across all syntactic structures (e.g., simple sentences, passive sentences, relative classes), the grammatical judgments of the deaf children who had learned ASL at an early age were more accurate than those of the deaf children who had not done so. In a subsequent study, children who were more proficient in ASL also scored higher on tests of English reading (Mayberry, 2007). Thus, it appears that learning a language early establishes a general foundation that can be engaged for later language learning and literacy.
L1 language skills also have been shown to promote a variety of school readiness skills in L2. Spanish language literacy and growth in Spanish vocabulary, for example, have been shown to contribute to the development of reading skills in English as an L2 (Rinaldi and Páez, 2008; see August and Shanahan  for a review). In a study of toddlers of low-income Mexican and Dominican immigrant mothers, rates of growth in the diversity of the children’s expressive vocabulary (words a child can produce) during book sharing (from ages 1 to 5 years) in either L1 or L2 predicted a variety of school readiness skills (narrative coherence, vocabulary, math skills, print knowledge) tested predominantly in English when children were 5 years of age (Tamis-LeMonda et al., 2014a). Cross-language facilitation
also was seen in a study of Latino/a English DLLs from low-income migrant families who were followed longitudinally from kindergarten to second grade to identify predictors of rate of growth in vocabulary (Leacox and Jackson, 2014). Although the low-income DLLs lagged behind their monolingual peers in vocabulary growth in English, high initial Spanish receptive vocabulary (words a child understands) at kindergarten was associated with greater growth in English receptive vocabulary over time.
In contrast to these studies of cross-language associations, correlations between measures of L1 and L2 and the ability to process information efficiently are sometimes seen only within languages (Marchman et al., 2010). In a test of speech processing efficiency and vocabulary development in 30-month-old Spanish-English DLL toddlers, children with larger Spanish vocabularies and faster processing speeds in Spanish did not process words faster in English. Similarly, Marchman and colleagues (2004) found in a study of 23.5-month-olds who were learning English and Spanish simultaneously that within-language were stronger than cross-language vocabulary-grammar associations.
In summary, several studies indicate that L1 development can facilitate L2 learning. Evidence in support of this finding comes from studies that report significant positive cross-language associations and transfer from L1 to L2 over time. DLLs typically show greater competence or dominance in one language; equivalent competence in both languages is rare. Differential dominance often can be explained by different amounts of exposure to each language (reviewed in the next section). The young language learner is still building the foundations of each language, and there is as yet little to transfer from the dominant to the nondominant language. Even so, once the young child builds a sufficiently strong base in L1, transfer between languages is likely to occur. The more advanced language learner is able to transfer or apply strong skills in one language to learning or using the weaker language. However, transfer is less likely to occur when language skills are underdeveloped.
Quantity and Quality of Language Input
Children’s development in both L1 and L2 depends on the language that is directed to them. Notably, infants and toddlers learn best under conditions of one-on-one interactions, in which talk is directed to them. Language simply overheard by toddlers has not been found to be related to growth in vocabulary or other aspects of language development (Ramírez-Esparza et al., 2014; Rowe, 2012; Weisleder and Fernald, 2013). Two features of language input and children’s language experiences that may affect DLLs’ early language development are examined in the following sections: (1) the quantity of exposure to each language; and (2) the quality of
language input, including the diversity of the input, contingent responsiveness, the speaker’s proficiency in the language, and engagement in literacy and learning activities (which offer children opportunities to hear diverse language and quantity of language).
Quantity of Exposure
As might be expected, children’s development in their L1 and L2 depends on the amount of exposure to each (e.g., De Houwer, 2009; Hoff et al., 2012; Place and Hoff, 2011; Song et al., 2012). A review of 182 empirical studies on DLLs indicated that differences among children in their language and literacy development depended on the quantity of their exposure to each language (Hammer et al., 2014), as well as when they were first exposed to their L2 (as discussed above in the section on timing of second language learning).
Most researchers who have examined the early vocabulary development of DLLs have found a significant association between exposure to each language and vocabulary size (e.g., Barnes and Garcia, 2013; Bialystok et al., 2010; De Houwer et al., 2014; Hoff et al., 2012; Oller et al., 2007; Thordardottir, 2011). In a set of studies with DLL toddlers exposed to Spanish and English, for example, estimates of input in each language were related to the percentage of words toddlers were reported to produce in Spanish and English (Hoff et al., 2012; Place and Hoff, 2011). These results are discussed in terms of associations between amount of exposure and proficiency. These researchers found that Spanish-English bilingual children with more exposure to Spanish than English generally achieved higher scores in Spanish than in English; those with more exposure to English than Spanish tended to achieve higher scores in English than in Spanish; and those with similar exposure to both achieved similar scores in each.
Hoff and colleagues (2012) demonstrated the role of relative exposure in the vocabulary and grammatical development of Spanish-English bilingual infants and toddlers in the United States. The parents of the bilingual and monolingual participants in this study had equally high levels of education and, importantly, most had college-level education. The children were assessed three times between 1 and 3 years of age. The monolinguals scored higher than the DLLs on measures of single-language vocabulary in English, the onset of combinatorial speech (two-word utterances), grammatical complexity, and mean length of utterance; this differential was evident at all three testing times and was estimated to correspond to about a 3-month lag for the DLLs. Notwithstanding group differences, there was considerable overlap in the English scores of the monolingual and DLL children. In fact, DLL participants who had had more than 70 percent exposure to English did not differ from the monolingual children who had had 100 percent ex-
posure. In contrast to the single-language results, no differences were found when the DLLs’ performance in both languages was considered together. In particular, there were no significant differences when total vocabulary in English and Spanish and combined speech in both English and Spanish were calculated.
Language exposure in each language also was found to be correlated with the vocabulary development of bilingual French-English 5-year-olds living in Montreal (Thordardottir, 2011) compared with monolingual French- and monolingual English-speaking children of the same age whose mothers did not differ from those of the bilingual children on education and nonverbal cognitive ability. The study findings revealed a strong and consistent association between exposure to a language and scores on vocabulary measures in that language, with more exposure producing higher scores, as expected. Similar findings have been replicated in longitudinal studies of children of other language backgrounds, including Basque and Spanish-French (Barnes and Garcia, 2013) and Finnish and Dutch (Silvén and Rubinov, 2010).
Beyond vocabulary, relative exposure to L1 and L2 also is related to measures of phonology and grammar. A study of Spanish-English DLLs ages 22 to 25 months (Parra et al., 2011) found that children’s relative amount of exposure to their two languages was related not only to their productive vocabulary size but also to their phonological memory and grammar in each language. The percentage of children’s home exposure to English was related to their nonword repetition accuracy for English-like but not for Spanish-like words. These findings show that relative exposure to L1 and L2 has language-specific relationships to phonological memory and that exposure effects are usually language-specific rather than cross-linguistic.
Although the above studies indicate that the proportion of exposure to each language predicts skills in vocabulary and/or grammar, they differ on estimates of just how much exposure is required to fully support children’s language development. In one study, no difference between DLL and monolingual 5-year-old children was found if the former had had at least 40-60 percent exposure to each language (Thordardottir, 2011). In contrast, even a difference of 10-20 percent in exposure to English was associated with reduced vocabulary scores in Spanish among a group of Spanish-dominant Spanish-English DLLs living in the United States who ranged in age from 16 to 20 months (Deanda et al., 2016). Similar results were found in English for English-dominant Spanish-English DLLs. These differences across studies may be attributable to the age of the children. The effects of exposure may be more pronounced among younger learners when the lexical system is relatively immature (Deanda et al., 2016). By implication, and as suggested by the results of Thordardottir (2011), differences may diminish and
even disappear with age as DLLs have more cumulative exposure to each language (see also Paradis et al., 2014).
As children’s exposure to a language increases, so does their speed at processing new information in the language. As is seen for vocabulary, associations between exposure and processing speed are language-specific. In one longitudinal study, Spanish-English bilingual children from families of a broad range of socioeconomic status were followed between ages 30 and 36 months, and their relative exposure to each language predicted their efficiency in real-time language processing and expressive and receptive vocabularies in that language (Hurtado et al., 2014). Thus, opportunities to practice real-time comprehension in a language sharpen processing skills as well.
Relative exposure to L1 and L2 also was found to affect the phonemic inventories of preschool-age children attending Head Start (Gildersleeve-Neumann et al., 2008). Monolingual English-speaking children ages 3-4 years were compared with English-Spanish bilingual children who either were exposed predominantly to English or received relatively equal exposure to both languages. Outcomes, including phoneme accuracy and error pattern frequencies, were measured over time. Children with the greatest cumulative exposure to English made the fewest errors, on average; conversely, children who were exposed to relatively more Spanish showed the highest maintenance of Spanish phonemic patterns and frequent vocalization errors in English, particularly syllable-level error patterns. Over time, however, rates of growth in phonetic skills were equivalent across the three groups.
When interpreting findings on relative language exposure, it is important to note that some of the previously discussed studies focused on the proportion of exposure to each language, whereas others focused on the absolute amount of exposure to each. Often, the proportion-based approach (for instance, that a DLL is hearing 40% English) leads to erroneous assumptions about the actual amount of language input. Moreover, people often assume that DLLs are, on average, exposed to less input in each language relative to monolinguals because they are exposed to two languages during the same time as monolinguals are exposed to one. However, a lower percentage of exposure does not necessarily mean less input. A DLL with half as much exposure to each language as a monolingual receives to one language could actually receive more input in one or both of those languages. If, for example, the Spanish-speaking parent of a Spanish-English DLL is more attentive to and talks more with her child than the Spanish-speaking parent of a monolingual child, the DLL may in fact experience more absolute language input than the monolingual child (see De Houwer et al.  for more discussion of this issue). Thus it is likely that the
amount of input, rather than the proportion of input, is the better predictor of DLLs’ proficiency in their L1 and L2.
Quality of Language Input
Studies of the quality of the language input DLLs receive, in contrast to their relative exposure to L1 and L2, have been limited. The features that define language quality change as children gain new skills in language and cognition over the course of their development. During the emergence of language (from about 10 to 18 months of age), word learning is slow. At this time, children benefit from hearing a large amount of language; a variety of words with which to label and describe objects, people, and events; language that is temporally contingent on their attention and communications; and relatively simple grammatical constructions. As children’s vocabularies and grammatical skills expand, between 18 months and 3 years of age, they continue to benefit from rich language input, particularly diversity in words and increasingly complex grammatical forms (Institute of Medicine and National Research Council, 2015). By around 3 years of age, children use and understand relatively decontextualized language that goes beyond the here and now, and they benefit from inferential questions that challenge them to reason about everyday situations and storylines in books (Kuchirko et al., 2015). By the pre-K years, children actively participate in give-and-take narrative exchanges and can co-construct personal narratives about the past and future, story narratives during booksharing, and fantasy narratives during pretend play (Uccelli et al., 2005).
The sections that follow examine some of these quality features of language, particularly those that support the language development of DLLs: the diversity of vocabulary to which children are exposed (that is, the number of different words in the input), the contingent responsiveness of language input, and caregiver engagement of children in literacy activities (with a focus on the use of questions during booksharing activities). Additionally, parents’ proficiency in the input languages can affect the quality of language addressed to children, which in turn can predict children’s language development. These factors are critical to consider in light of growing evidence that it is the quality of language directed to children that most strongly influences language development (Golinkoff et al., 2015), even after controlling for the sheer amount or quantity of language input (Rowe, 2012).
Diversity of the input The diversity of parental language (across and within different levels of socioeconomic status), reflected in the use of different word types and the different ideas conveyed by those words, is positively associated with children’s vocabulary size, rate of vocabulary growth (e.g.,
Hart and Risley, 1995; Hoff, 2003, 2006; Tamis-LeMonda et al., 2012a), phonological awareness, listening comprehension (Sénéchal et al., 2006), cognitive skills, preacademic skills, and school performance (Marchman and Fernald, 2008). Although most studies on the benefits of parents’ lexical diversity for children’s language development focus on monolingual children, their findings extend to DLLs as well. In a longitudinal study of DLLs of Mexican and Dominican descent, low-income immigrant mothers’ increased use of different word types during booksharing with their 2- to 5-year-old children was associated with children’s vocabulary growth in the respective language. In turn, children’s language skills predicted their narrative skills, emergent literacy, and emergent math at 5 years of age (Tamis-Lemonda et al., 2014a). In another study, Latino mothers of Spanish-learning infants varied substantially in the quantity and diversity of their language input to their children. Infants of relatively talkative mothers heard three times as many different words and more complex sentences as did infants of less talkative mothers, and these differences related to the children’s vocabulary size at age 2 (Hurtado et al., 2008). These results also corroborate arguments made previously that the percentage of exposure to L1 and L2 may not be the most useful measure of the amount of exposure to each.
Exposure to rich language early in language development is especially important because it facilitates children’s skills at real-time language processing and consequently vocabulary building. In one study of Spanish-speaking Mexican families of low socioeconomic status, the amount of speech directed to infants predicted how efficiently they processed familiar words in real time, based on a measure of how quickly they became oriented to pictures of familiar words. It also was associated with the children’s expressive vocabularies at 24 months (Weisleder and Fernald, 2013).
Additionally, the ways in which parents use language—referred to as the pragmatic functions of language—can influence children’s language development by affecting the complexity of sentence structures, as well as children’s opportunities to participate in conversations. Parents who frequently use commands and directives (also referred to as regulatory language) may cut short the rich vocabulary and conversational turn taking that occurs when they ask questions. Asking a child, “What do you want to do next?” is more likely to elicit a conversational response than is “Do that.” This point is illustrated by a study in which supportive language input to 2- and 3-year-olds (in families of middle to high socioeconomic status) took the form of conversations in which mothers asked their children questions and engaged them in conversational exchanges (Hoff, 2006).
An analysis of the use of child-directed language by low-income immigrant U.S. Latino mothers of 2-year-old DLLs showed that directive/regulatory language contained a preponderance of pronouns, whereas refer-
ential language—in which mothers used language to talk about objects and events in everyday life—contained many nouns, adjectives, verbs, and adverbs. In turn, referential but not regulatory language was related to the size of DLL toddlers’ expressive vocabularies in English and Spanish (Tamis-LeMonda et al., 2012b). The grammatical complexity of parental language, including the variety of different syntactic structures in which verbs appear, likewise predicts monolingual children’s vocabulary (Hoff, 2003; Hoff and Naigles, 2002) and grammatical development (Huttenlocher et al., 2010), although comparable research on DLLs is scarce.
Contingent responsiveness Responsive language experiences, defined as input that is prompt, contingent, and positively connected to a child’s interests and actions, predict gains in monolingual children’s language, especially during the first 2 years of life (e.g., Bornstein et al., 2008; Landry et al., 2006). Contingent responses to infant behaviors promote word learning by increasing the likelihood that infants will hear words that are the focus of their attention, thereby reducing referential ambiguity and easing the mapping of words to objects and events in the environment (Tamis-LeMonda et al., 2014b). One study with DLL toddlers of Spanish-speaking Dominican and Mexican immigrant mothers found that the mothers were contingently responsive to the toddlers; when the toddlers touched or acted on objects, the mothers followed with labels and descriptions for those objects within 2 seconds (Tamis-LeMonda et al., 2013).
The importance of contingent responsive language input for children’s language development is likely due to children’s ability to learn words for things and events that interest them and are already the focus of their attention (Hirsh-Pasek et al., 2015; Konishi et al., 2014). Consequently, it has been found that children whose parents talk to them about what interests them have more advanced vocabularies than children whose parents frequently redirect their attention and label objects that are not of interest to them (e.g., Konishi et al., 2014). Although research in this area is based primarily on the experiences of monolingual children, there is mounting evidence for the supportive role of contingently responsive language in the language development of DLLs (e.g., David and Wei, 2008).
Speaker’s proficiency For DLLs, as for monolinguals, the proficiency of a caregiver’s language skills in L1 and L2—including the use of correct grammatical forms and diverse vocabulary—powerfully affects their language trajectories in each language. Caregivers who engage with their children in a language in which they are proficient and with which they are comfortable may also benefit their children socially.
Many immigrant parents use English with their children with the aim of supporting their children’s English language development. However,
parents’ proficiency in English has been found to determine whether this strategy is effective. Parental English language proficiency is often measured through parent report—by asking parents to rate how well they understand, speak, write, and read English (as separate questions), or asking them to rate their proficiency level on a scale ranging from having few words or phrases (low proficiency) to native-like proficiency with good vocabulary and few grammatical errors (high proficiency) (e.g., Baker, 2014; Goldstein et al., 2010). However, many DLLs are not exposed to proficient English. More than 40 percent of Latino children, for example, have at least one parent with limited English proficiency (Hernandez et al., 2007b); children of Mexican, Dominican, and Central American descent in particular are less likely to have parents who are proficient in English relative to other Latino children whose parents have different educational backgrounds, are bilingual, and are of different generational status in the United States (Hernandez, 2006).
When the source of input for one or both of a DLL’s languages is a non-native speaker, the child may hear grammatical forms that deviate from monolingual norms and in turn may reproduce these forms. In a case study, for example, a Spanish-English bilingual child who used many more overt subjects in Spanish than is typical of Spanish monolingual children actually heard more overt subjects in the Spanish used by her English-speaking mother, who was a non-native speaker of Spanish (Paradis and Navarro, 2003) (see De Houwer [2009, pp. 285-286] for synopses of other studies that have found a relationship between adult usage and DLLs’ productions).
A DLL can benefit from hearing English early in development from a parent who is comfortable with and competent in English (Kovelman et al., 2008a). Use of L2 by immigrant parents promotes children’s language development only if the parents have achieved a threshold level of proficiency in that language (Paradis et al., 2011a). For simultaneous Spanish-English DLLs, the proportion of input that is provided by native speakers of English predicts their English skills after controlling for the total amount of language exposure (Place and Hoff, 2011). Conversely, when parents are limited in English proficiency, talking to their children in English can also compromise the children’s native (L1) language development without yielding significant gains in English (Hammer et al., 2009; McCabe et al., 2013; Paradis et al., 2011a).
Parental English language proficiency also was found to relate to children’s segmental accuracy on phonological production tasks (i.e., the percentage of consonants and vowels children produce correctly) in a sample of 5.9-year-old Spanish-English DLLs (Goldstein et al., 2010). In another study, associations between Mexican mothers’ English proficiency and their preschoolers’ reading and math scores were examined in a nationally representative sample (Baker, 2014). Mothers’ English proficiency predicted their
children’s reading (but not math) achievement as a result of its influence on the mediating variable of home literacy involvement in English. Thus, DLLs’ education and development may be enhanced by programs aimed at enhancing mothers’ English proficiency and home literacy activities.
In a related vein, and as noted earlier, speaker proficiency also relates to DLLs’ ability to learn associations between new words that comprise minimal phonemic pairs and their referents during early language emergence. Infants who are learning one language succeed at such tasks around 17 to 20 months of age, whereas infants learning two languages from birth do not succeed until 20 months of age (Fennell et al., 2007; Werker et al., 2002). However, follow-up research (Fennell and Byers-Heinlein, 2014; Mattock et al., 2010) indicates that success on this demanding task may depend on whether pronunciation of the novel words to be learned in the study matches the language environment in which the children were actually learning language. Early abilities to discriminate among specific phonemes are affected by the phonetic properties of caregiver speech (Fennell and Byers-Heinlein, 2014).
Over time, DLLs who speak their L1 and are exposed increasingly to their L2, typically English, often as a result of schooling in L2 and/or contact with native speakers of that language, often show an increasing preference for using L2 (see also Chapter 6 for a discussion of reclassification issues in grades K-12). Consequently, the L1 may begin to weaken, resulting in deviations in the speakers’ underlying knowledge and their differential use of specific grammatical structures and constraints compared with typical monolingual patterns (Montrul, 2008). The importance of parents’ language proficiency for DLLs’ language development extends into adulthood. Jia and colleagues (2002) found that the L2 skills of adults who were immigrants as children depended on their immigrant parents’ fluency in English.
Parents’ language proficiency also is important for the quality of parent-child interactions more broadly, which in turn can influence children’s language learning. Parents may inadvertently limit their ability to convey certain information to children when they communicate in a language they do not know well (McCabe et al., 2013). Children enjoy better relationships with their caregivers (Oh and Fuligni, 2010) and are less likely to be alienated from them (Tabors, 1997) when they are able to communicate in their parents’ heritage language (McCabe et al., 2013).
The social and cognitive benefits that have been documented in children fluent in two or more languages, discussed earlier, speak to the importance of maintaining skills in L1 to promote bilingual proficiency. Often, however, the integration of immigrant families into a predominantly English-speaking society can lead to a shift from a non-English primary language to English over generations (National Task Force on Early Childhood
Education for Hispanics, 2007). Therefore, as English becomes part of the child’s experiences, the issue of L1 preservation becomes more relevant to understanding development and learning. Use of the first language in various settings, for example, is associated with the development of a healthy ethnic identity in early childhood (Bialystok, 2001) and mitigates the potential negative psychological effects of losing L1 and weakening relationships with parents and family members (Tseng and Fuligni, 2000; Wong-Filmore, 2000). The formation of cultural identity also is related to language use (Espinosa, 2010a). Loss of L1 may compromise children’s sociocultural understanding of and appropriate interactions in the families and communities in which they reside. In some cases, moreover, loss of the L1 has been associated with a sense of shame or disregard for the family’s culture, furthering minimizing developmental opportunities (Hakuta and D’Andrea, 1992; Wong-Fillmore, 1991).
Engagement in literacy and learning activities Children’s participation in literacy activities such as shared book reading, storytelling, reciting nursery rhymes, and singing songs supports their language growth and emergent literacy in several ways. There is ample evidence for the benefits of shared book reading and exposure to print with respect to children’s vocabulary size, phonemic awareness, print concept knowledge, and positive attitudes toward literacy (Bus et al., 1995; Dickinson and Tabors, 1991; Lyytinen et al., 1998; Raikes et al., 2006; Sénéchal et al., 1996; Snow and Dickinson, 1990; Wagner et al., 1994; Watson, 2001). In particular, research indicates strong associations between dialogic reading—adults’ use of “wh” questions and informative feedback during booksharing—and children’s language skills within and across developmental time (Reese and Newcombe, 2007; Sénéchal, 1997; Whitehurst et al., 1988, 1994). Additionally, dialogic reading relates to children’s independent storytelling skills, emergent literacy, vocabulary growth, print awareness, and memory (Fiorentino and Howe, 2004; Kang et al., 2009; Schick and Melzi, 2010).
The benefits of dialogic reading generalize to DLL preschoolers (Kuchirko et al., 2015; Luo and Tamis-LeMonda, 2017). For instance, Latino DLL preschoolers whose teachers encouraged them to co-construct stories from wordless books (i.e., adopting a dialogic booksharing style) demonstrated superior print-related language and storytelling skills at the end of the preschool year compared with DLL preschoolers whose teachers did not adopt this style (Schick, 2015). It appears, however, that DLLs engage in literacy and other learning activities less often than monolingual children, which may contribute to the relatively low performance of some DLLs in school. Many explanations for these disparities in literacy and learning experiences are possible, including concentrated disadvantage experienced by many families with DLLs and low access to books in lan-
Notably, findings of comparatively low literacy activities in some Spanish-immigrant families are not always replicated in studies involving other immigrant groups. One study found that Asian DLL parents endorsed reading books at bedtime more frequently than did Euro-American parents. Their children also were significantly more involved in preacademic activities such as learning letters, numbers, and math skills; playing alphabet and number games; engaging in computer activities; and visiting the library (Parmar et al., 2008). These findings, however, may be explained by differences in socioeconomic status across studies; for example, the Asian immigrant families in this study were from middle- to high-income backgrounds. It also is important to note that Asians who immigrate from some countries in Southeast Asia (e.g., Hmong, Cambodia, Mynamar) show patterns similar to Spanish-immigrant families who have lower levels of education and fewer economic resources (see, e.g., Council on Asian Pacific Minnesotans, 2012).
Television and other technologies There is a paucity of research on the potential role of electronic tools in DLLs’ learning since most such studies are conducted with monolinguals. Nonetheless, work on television viewing in relation to toddlers’ language learning has shown few benefits (Linebarger and Walker, 2005) and even some impairment of learning (Hudon et al., 2013). Similarly, electronic board books have limited learning benefits for toddlers (Sosa, 2016). In contrast, electronic books, educational programs, and computer apps may provide opportunities for DLLs, particularly those who ordinarily experience little exposure to English, to hear proficient English (e.g., Leacox and Jackson, 2014). However, evidence showing that apps do not help monolingual infants and toddlers learn language (Roseberry et al., 2014) suggests that their DLL counterparts are unlikely to benefit. Nonetheless, additional research is needed on this question.
Cross-Linguistic Influences of L1 on L2 Learning
While the evidence reviewed in the first section of this chapter indicates that for the most part, DLLs keep their languages separate, at times they differ from monolinguals in their language usage in ways that can be attributed to cross-linguistic influences. There is no evidence that cross-linguistic influences are pervasive (i.e., broad in scope) or long-lasting, except possibly in the case of children who acquire an L2 after their L1 (see Meisel  and Paradis et al. [2011b] for reviews). Evidence of such influences is discussed in this section.
Because languages of the world vary in the extent to which they differ in structure, a critical task for parents and teachers of multilingual English learners is to understand how development in the components of a child’s native language may affect the acquisition of English. If for example, the child’s native language is similar to English (e.g., Dutch), initial learning of English may be easier than if the native language is different from English (e.g., Hmong). Indeed, cross-language similarities and differences may account for some of the discrepant findings on transfer of skills from L1 to L2 reviewed above, and may influence children’s rate of learning a second language and ultimate level of proficiency discussed earlier.
Influence of L1 on L2 Speech Perception
After a certain age, humans’ phonological representations are fairly fixed. There is a major gap in the literature, however, on what that age is for English contrasts that do not exist in other languages (such as ship versus sheep for native Spanish speakers). Empirical evidence on how English L2 speech perception becomes more difficult as a function of age and whether certain contrasts are more difficult at certain ages and for speakers of certain native languages could provide information on the optimal instruction for DLLs of different ages with different L1 backgrounds. Older children have been shown to improve their perception and identification of non-native vowel sounds with as a little as 5 hours of training, and such training has been shown to be more effective for 7- to 8-year-olds than for adults (Giannakopoulou et al., 2013). Similarly, a study of phonological production and perception found that Korean children surpassed Korean adults in the production of certain English vowels, supporting the idea that the older L2 learners are, the less likely they are to be able to establish new vowel categories needed for accurate L2 vowel production and perception (Baker et al., 2008). This is yet another area in which the evidence strongly suggests that earlier exposure leads to better L2 learning. But more evidence is needed on effective techniques for speech perception training for children of different ages who are native speakers of different languages (e.g., Spanish vs. Mandarin).
Morphological differences in the L1s of DLLs (e.g., Spanish versus Hmong) may result in different patterns of English (L2) learning. Hmong, for example (unlike English and Spanish), is a tone language in which morphological structures such as plurals are marked lexically instead of by suffixes. A number of studies have examined how native Hmong-speaking preschoolers who begin to learn English in preschool learn words in Eng-
lish and in their native Hmong (Kan, 2014; Kan and Kohnert, 2008). After these children had been exposed to English for 6 months, there was no evidence that they could learn words in English as quickly as they did in their native Hmong (Kan and Kohnert, 2008). After the children had been exposed to English for 14 months, they still recalled more words in their native Hmong than in English (Kan, 2014). Subsequent analyses showed that knowledge of L2 predicted children’s ability to retain the new words they learned in L2. Thus, these findings indicate that Hmong children’s ability to learn and retain words quickly in L2 depended on other aspects of their L2 knowledge. One potential explanation for why native Hmong speakers do not appear to benefit from their L1 vocabularies when learning English as their L2 may be phonological and morphological differences between Hmong and Spanish (versus English). In contrast with English and Hmong, there may be sizable overlap between Spanish and English sounds with high phonotactic probabilities and the ways in which plurals are made.
The structure of the words children learn—reflected in the structure of the input they receive—also may influence their development of proficiency in English as a second language. Studies of children learning only one language strongly suggest that language learning builds on itself (e.g., Reznick and Goldfield, 1992). The language-learning environment consists of many different kinds of statistical regularities, among words themselves as well as among words and kinds of entities in the world. Children learning one language have been shown to be highly sensitive to these regularities and to use them to learn new words (Gathercole and Min, 1997; Gleitman, 1990; Golinkoff and Hirsh-Pasek, 2006, Imai and Gentner, 1997; Pinker, 2013; Waxman, 2009; Yoshida and Smith, 2003). By implication, another reason for different patterns of L2 (English) learning by DLLs who speak different L1s may involve the composition of their early vocabularies. Children learning Korean, Mandarin, and other East Asian languages as their native language often show a “verb bias,” or a tendency to learn words for actions before learning words for solid objects (Choi and Gopnik, 1995; Tardif, 1996, 2017; Tardif et al., 1997)—a pattern that contrasts with that generally found in native monolingual English speakers (Nelson et al., 1993). Perhaps learning an L1 that emphasizes different word classes than English (i.e., nouns or verbs, either through frequency or word position) poses a greater challenge to certain L1 groups learning English as an L2.
Influence of DLLs’ Grammars on One Another During Development
One salient type of cross-linguistic influence in DLLs is the substitution of a word order rule from one language to the other. In a study on young Cantonese-English DLLs (ages 2 to 4 years) in Hong Kong, Yip and Matthews (2007) noted the placement of relative clauses before the noun they modified. They found that their Cantonese-dominant participants used the relative clause word order of Chinese rather than that of English. For example, the children would ask, “Where’s the Santa Claus give me the gun?” instead of the target English form, “Where’s the gun that Santa Claus give (gave) me?” (Yip and Matthews, 2007, p. 155). Nicoladis (2002, 2003) also found cross-linguistic influence in French-English children’s use of compound words. The order in which such words are created is usually the opposite in French and English—for example, brosse à dents (brush-teeth) in French versus toothbrush in English. Nicoladis found that French-English bilingual children were more likely than monolinguals to reverse the word order in their compound words in both languages.
Cross-linguistic influences also have been noted that alter the frequency of DLLs’ usage of optional but correct grammatical patterns relative to monolinguals. Paradis and Navarro (2003), for example, examined the use of sentential subjects by a Spanish-English DLL girl from the age of 1 year, 9 months to 2 years, 6 months compared with that of Spanish monolinguals of a similar age. The Spanish-English DLL girl in this study used more overt subjects in her Spanish sentences—subjects that were sometimes redundant in the conversation—relative to two Spanish monolingual children her age. The authors suggest that the child was more likely to use subjects in her Spanish than is typical among monolingual Spanish-speaking children because English requires a subject.
How long do cross-linguistic influences persist in development? Some researchers, such as Yip and Matthews (2007), have documented the increase and then decline of certain cross-linguistic structures in the language of DLLs over time during the preschool years. Studies of simultaneous bilinguals provide evidence that some aspects of cross-linguistic influence are temporary, but research with school-age second language learners suggests that these influences can be more extended. Serratrice and colleagues (2009) asked Italian-English DLLs ages 6 to 10 years and their monolingual peers to judge whether certain plural noun phrases were grammatical. The DLLs, even those in the oldest group, showed some cross-linguistic influence in their performance on this task because they sometimes accepted noun phrases as grammatical in one language when those phrases actually had the morphosyntactic structure of the other language. Such research suggests that interactions between dual language systems may be a permanent feature of sequential DLLs’ grammars.
The broader sociocultural context in which DLLs grow up influences their language development, especially those aspects that are valued and rewarded in school settings. An ecocultural approach to language learning highlights the intersecting multiple contexts in which children develop (Bronfenbrenner, 1979; Weisner, 2002) and the shared values and practices of cultural communities that affect their language-learning experiences (Heath, 1982; Tamis-LeMonda and Song, 2012). Parents from different cultural communities, and even those within the same cultural group, provide different language experiences to their DLL children, and these differences play out in children’s language development, school readiness, and later academic success, as reviewed earlier. Moreover, DLLs may be exposed to more than one language in the home and other informal educational settings, and those settings may be characterized by aspects of the immigrant experience and other risk factors, such as poverty, low levels of parental education, and lack of access to resources that support literacy. These circumstances are important given that language practices in home, neighborhood, and school settings are highly relevant to early language and literacy outcomes (Goldenberg, 2006; Nord and Griffin, 1999; Tabors, 1997; Tabors et al., 2001).
As described in Chapter 3, DLLs in the United States are on average more likely than monolingual English-speaking children to live in poverty and to have parents with limited formal education, especially if their parents are recent immigrants. Living in poverty, however, does not necessarily lead to poor outcomes. It is critical to contextualize these vulnerability factors, recognizing that in general, developmental and educational vulnerability is attributable not only to characteristics of DLL families such as low parental education, but also to many interrelated entities and factors outside the family, including the quality and resources of the neighborhood and schools and the value society ascribes to different foreign languages, as well as national differences in the value attached to multilingualism. The following sections review research relevant to these issues (see Box 4-3).
Cultural Practices Regarding Communication
Parents from different communities and ethnicities display similarities and differences in their communicative interactions with children, with many such practices being rooted in cultural norms and beliefs (Schieffelin and Ochs, 1986; Tamis-LeMonda and Song, 2012). Parents generally are similar in relying on spoken language, as well as nonverbal forms of communication including gaze, touch, and gesture, to communicate with their
children, yet differ in their relative emphases on these various modes of communication.
Parents of different cultural backgrounds also are similar in communicating about objects, events, actions, and the experiences of self and others using grammatical forms (e.g., nouns and verbs) that map onto fundamental, universal concepts. However, they vary in the content (i.e., topics) of their communications—for example, in their differential use of language as a tool to impart knowledge versus to regulate child behavior. Thus, both the forms (structure and content) and functions (purpose) of parent-infant communications are products of culture.
Use of gesture is one aspect of communication that varies across cultural communities. Gestures (such as pointing) that accompany words can help children who are first learning language to match words to referent objects by “narrowing the search space” and enabling children to perceive the word and stimulus as “belonging together” (Rader and Zukow-Goldring, 2010). Research has shown that gestures support English-speaking monolingual children’s word learning (e.g., Rowe and Goldin-Meadow, 2009) and also predict cognitive skills in DLL Latino toddlers (Tamis-LeMonda et al., 2012b). Gestural communication may be especially prevalent in certain cultural communities. In particular, a high reliance on such communication has been documented in certain Latino (particularly Mayan) communities, in which much of children’s learning occurs through “keen observation” of the people around them (Rogoff et al., 2003). One study found that 2-year-old U.S. children of Mexican immigrant mothers displayed more gesture use and higher skills at sequencing and imitating actions and following commands that incorporate gestures (despite lower expressive language) relative to children from other ethnic backgrounds during their first 2 years (Tamis-LeMonda et al., 2012b). When social interactions between Mexican and Dominican DLLs of low-income backgrounds were compared with those of monolingual children from low-income African American backgrounds, Mexican immigrant mothers in particular were found to be most responsive to the gestures produced by their infants relative to mothers in the other groups (Tamis-LeMonda et al., 2012b), and used gestures frequently to teach their toddlers a new task of how to string beads (Luo and Tamis-LeMonda, 2016). Reliance on gesture as a communicative tool can aid language learning if gestures are coupled with child-directed speech, but impede language learning if they substitute for language inputs. It is important to consider how children and parents from different cultural backgrounds communicate in ways beyond spoken language when interpreting differences in spoken language among DLLs from different cultural backgrounds.
Beyond the family, features of communities and neighborhoods create or restrict opportunities to foster DLLs’ learning, use of language, and sense of identity. These features encompass community elements both structural (physical spaces shared by people) and psychological (beliefs, values, history, and practices shared by people).
The extent to which the home languages of DLLs are valued in their communities is a key aspect of these children’s daily lives. Researchers have distinguished between mature and immature immigrant-receiving communities (Urzúa and Gómez, 2008). Mature communities are more likely than immature ones to have a longer history of being a relocation area for immigrant groups. As a result, they may have community resources that serve the basic needs of immigrants (e.g., housing and employment opportunities) and foster a sense of community within immigrant groups, as well as positive attitudes toward bilingualism (Urzúa and Gómez, 2008). In contrast, immature immigrant-receiving communities may have a shorter history as relocation areas and thus have fewer resources for immigrant groups, which can create a sense of isolation and limit opportunities to speak the home language with other people.
The presence and value of different languages in a community can be observed within a community’s shared spaces (e.g., neighborhoods, city blocks, town limits) and specific community structures (e.g., playgrounds, community resource centers, churches, grocery stores)—spaces where people who live in the community come together and interact. Such opportunities for diverse and frequent linguistic interactions increase the likelihood that DLLs will become bilingual and biliterate. Reese and Goldenberg (2006) found that in neighborhoods where most signs were written in both English and the community members’ native languages and where native languages were used frequently in commercial transactions and community activities, DLLs were more likely to acquire the native language.
Community influences are illustrated by a study of family access to printed materials across 35 communities in the United States. Communities with high concentrations of Latinos were less likely to have printed materials, and available materials were more likely to be in Spanish, relative to communities with higher income and education levels, which had access to more literacy materials in English (Reese and Goldenberg, 2006). Additionally, low-income communities have fewer print resources available to children relative to middle-income communities, placing children from poor households (a disproportionate number of which are dual language households) on divergent paths to literacy and language development well before they start school (Neuman and Celano, 2001). These inequities span the quantity and quality of literacy materials, public spaces and places
for reading, and even the types of literacy materials available at public institutions such as child care centers and libraries (Neuman and Celano, 2001). In turn, community (together with family) language characteristics were related to the literacy outcomes in Spanish and English of children in kindergarten and first grade. Thus in early stages of children’s literacy development, communities can influence Spanish-speaking children’s literacy through language-learning opportunities.
Parents of DLLs can promote a sense of community through their efforts to socialize their children in ways that maintain important features of their culture of origin (Hughes et al., 2006). Immigrant parents may seek out community organizations that offer L1 classes, schools in which the curriculum of the country of origin is taught, or religious institutions that promote children’s ethnic and cultural identity. These goals for cultural maintenance may encourage parents of DLLs to select neighborhoods or communities that afford their children opportunities to interact with other children and families from their cultures of origin. In a study of Chinese language schools in Chicago, Lu (2001) found that parents sent their children to Chinese schools as a way of maintaining their Chinese identity, by learning Chinese and participating in community activities. Similarly, Inman and colleagues (2007) found that Indian Asian immigrant parents brought their children to religious activities as a way of preserving their ethnic identity. Such socialization practices of parents of DLLs may shift through successive generations as families move from ethnic enclaves to more diverse neighborhoods and as they gain an understanding of U.S. racial stratification (Hughes et al., 2006).
A number of factors have been shown to influence the development of dual language proficiency. Early relative to later exposure to English as a second language can facilitate its learning if the language being heard is spoken by speakers who are fluent and proficient. It is also critically important, however, for young children who are beginning to learn an L2 a few years after birth to continue to develop their L1, as many cases of positive transfer from L1 to L2 have been documented when L1 is strong. Literacy experiences such as book reading also are associated with diverse and rich language that promotes language skills in children. Parents’ immigrant generation status and education, the status of L1 in the community, and neighborhood features all relate to parents’ use of language with their children and with the children’s language skills. Parents from different cultural communities have differing views and practices concerning their role as teachers of their children and how much and how they communicate
with their children (including variations in gesture use and other nonverbal modes of communication). These differences influence children’s language development insofar as they affect how parents and others use language, communicate, and interact with DLLs.
Conclusion 4-1: Children learning two languages from birth or within the first 3 years of life exhibit many similarities with monolingual children in their developmental trajectories and their skills in each language. At the same time, those trajectories or outcomes can differ between the two groups. Dual languages learners (DLLs) may take longer to learn subtle aspects of language that differ between the two languages, they may use alternative learning strategies to manage input from the two languages, and their levels of proficiency may reflect variations in language input and its quality. Even though these differences sometimes result in DLLs sounding different from monolingual children of the same age, these differences are in most cases normal and typical for children learning two languages at the same time, and not an indication of disorder, impairment, or disability.
Conclusion 4-2: There is no evidence to indicate that the use of two languages in the home or the use of one in the home and another in an early care and education setting confuses dual languages learners or puts the development of one or both of their languages at risk. Given adequate exposure to two languages, young children have the capacity to develop competence in vocabulary, morphology, syntax, and pragmatics in both.
Conclusion 4-3: Children given the opportunity to develop competence in two or more languages early in life benefit from their capacity to communicate in more than one language and may show enhancement of certain cognitive skills, as well as improved academic outcomes in school.
Conclusion 4-4: The cognitive, communicative, cultural, and economic benefits of knowing English and another language are most likely to occur when individuals have high levels of linguistic and functional competence in both languages, including speaking, listening, reading, and writing in both. This is most likely to occur if development of the home language is maintained throughout the preschool and school years as dual languages learners learn English.
Conclusion 4-5: Research indicates that children’s language development benefits from the input of adults who talk to them in the language in which the adults are most competent and with which they are most comfortable. Dual languages learners’ (DLLs’) language development, like that of monolingual children, benefits from the amount and quality of child-directed language—that is, language that is used frequently in daily interactions, is contingent on the child’s language and focus of attention, and is rich and diverse in words and sentence types. For most DLL families, this quantity and quality of child-directed language are more likely to occur in the home language, not English.
Conclusion 4-6: Dual language learners’ language development can benefit from shared book reading and storytelling that are characterized by diverse and rich language that promotes interaction and engagement between another person and the child. Infants and toddlers have not been shown to learn language from television or computer applications that do not involve interactions with other people.
Conclusion 4-7: Language competence varies considerably among dual language learners. Multiple social and cultural factors—including parents’ immigrant generational status and years in the United States, socioeconomic status, exposures to the risks of poverty, the perceived status of the home language in the community, and neighborhood resources—may help explain this variation.
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