The hypothesis was tested that children whose families differ in socioeconomic status (SES) differ in their rates of productive vocabulary development because they have different language-learning experiences. Naturalistic interaction between 33 high-SES and 30 mid-SES mothers and their 2-year-old children was recorded at 2 time points 10 weeks apart. Transcripts of these interactions provided the basis for estimating the growth in children's productive vocabularies between the first and second visits and properties of maternal speech at the first visit. The high-SES children grew more than the mid-SES children in the size of their productive vocabularies. Properties of maternal speech that differed as a function of SES fully accounted for this difference. Implications of these findings for mechanisms of environmental influence on child development are discussed.Family socioeconomic status (SES) is a powerful predictor of many aspects of child development. An aim of current research is to identify the pathways by which SES exerts its well-established influence (DeGarmo, Forgatch, & Martinez, 1999;Keating & Hertzman, 1999;Linver, Brooks-Gunn, & Kohen, 2002; National Research Council and Institute of Medicine, 2000). Because SES and child development are multifaceted variables and because many factors that influence child development covary with SES, the causal relations underlying SES effects on child development may be difficult to uncover (Hoff, Laursen, & Tardif, 2002). The present study focused on one reliably observed relation between SES and child development and sought to identify the underlying mechanism.The relation in focus is that between SES and early vocabulary development. It is well established that children from lower SES build their vocabularies at slower rates than children from higher SES (Arriaga,

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On average, children from low SES homes and children from homes in which a language other than English is spoken have different language development trajectories than children from middle class, monolingual English-speaking homes. Children from low SES and language minority homes have unique linguistic strengths, but many reach school age with lower levels of English language skill than middle class, monolingual children. Because early differences in English oral language skill have consequences for academic achievement, low levels of English language skill constitute a deficit for children about to enter school in the U.S. Declaring all developmental trajectories to be equally valid would not change the robust relation between English oral language skills and academic achievement and would not help children with poor English skills to be successful in school. Remedies aimed at supporting the development of the English skills required for academic success need not and should not entail devaluing or diminishing children’s other language skills.

The contributions of social processes and computational processes to early lexical development were evaluated. A re-analysis and review of previous research cast doubt on the sufficiency of social approaches to word learning. An empirical investigation of the relation of social-pragmatic and data-providing features of input to the productive vocabulary of sixty-three 2-year-old children revealed benefits of data provided in mother-child conversation, but no effects of social aspects of those conversations. The findings further revealed that the properties of data that benefit lexical development in 2-year-olds are quantity, lexical richness, and syntactic complexity. The nature of the computational mechanisms implied by these findings is discussed. An integrated account of the roles of social and computational processes to lexical development is proposed.

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