ings. The available research is quite limited. In their study of “what works” for English language learners in adult literacy education, Condelli and Wrigley (2004) identified only one study of ESL students that measured a literacy outcome and included a design without confounds. Similarly, Torgerson and colleagues (2004) examined almost 5,000 reports on adult literacy and numeracy interventions, and only 3 randomized controlled trial designs focused on English as a second language. Adams and Burt (2002) cast a much wider net in their search for research on adult language learners between 1980 and 2001 to include experimental, descriptive, and practitioner studies from journals, books, reports, and dissertations. The 44 studies reviewed had methodological weaknesses, such as too few participants, unreliable measures, inadequately described practices and outcomes, and no comparison tasks or groups, which prevented drawing conclusions about the effectiveness of the approaches. Several of the studies focused on language learners in English preparatory classes before attending college, who are likely to differ in several ways (education level, first language literacy proficiency, socioeconomic status) from the broader population of English language learners. These results are consistent with a recent review of adult literacy instruction research available from the U.S. Department of Education (Kruidenier, MacArthur, and Wrigley, 2010). Similarly, the committee located four studies (two of adults in adult education and two of students in developmental college education courses) from 1990 to 2010 with the criterion that the research include at least one quantitative measure of literacy skill (see Appendix C). Because studies are so few and the ones available suffer from various methodological constraints, it is not possible to draw strong conclusions about effective instructional practices.
Given the limited research on the literacy development of adult English language learners in the United States, we also draw from a broader base of knowledge on second language and literacy development, which includes relatively well-educated adults and young children in K-12 education. Because a main challenge of literacy development for this population is learning a second language, we review research related to the development of both spoken and written language.
For simplicity, we use the term English language learners in this chapter to refer to foreign-born and native-born adults who are developing their English language skills and refer to other adults as native English speakers. On occasion we use more specific terms provided by study authors when referring to individual research studies. The research and sources of information reviewed in this chapter often do not include, however, precise or consistent ways of defining particular subgroups of the English learner population. In future research, more standard terms and definitions will be needed to refer to segments of this population to facilitate the accumulation of reliable, valid, and more interpretable research findings.