speculated, since being a minority and English-language learner in the United States is confounded with SES, vocabulary probably also affects achievement gaps for those groups to some degree.
Another well-established finding is that vocabulary predicts how well all children will do in school, regardless of SES: after controlling statistically for SES and SES-related factors (such as nutrition), vocabulary still matters for school achievement. According to Hoff, this finding points to the vital importance of vocabulary because, theoretically, if SES and those other SES-related factors measured in those studies were somehow magically fixed, children with larger vocabularies would still perform better in school. Yet, Hoff was not aware of any studies that have included the analyses needed to test more directly whether vocabulary helps to explain the correlation between SES and achievement. Nor is there evidence about how much of the difference in achievement between lower and higher SES students can be attributed to vocabulary.
Experimental research also has not been conducted to test whether the SES-related achievement gap could be narrowed by increasing vocabulary. Nor has there been any research on how much the gap would be narrowed by addressing vocabulary directly—rather than other known SES-related influences on achievement, such as nutrition.
The literature does suggest, however, some sources of SES-related differences in vocabulary that might have implications for intervention, Hoff said. One possible focus for intervention is the amount of language input experienced by children of different socioeconomic backgrounds. This claim has sometimes been subject to controversy but it is derived from several findings.1
First, studies show that vocabulary size and growth are associated with the amount and complexity of language children hear in their everyday lives. Children from lower SES homes who, on average, have smaller vocabularies hear less language and less complex language at home than children from more economically advantaged backgrounds (Hart and Risley, 1995; Hoff, 2003, 2006, 2009). If children hear two languages at home, they have larger vocabularies in the language they hear most, suggesting again the importance of amount of language input to language learning.