Early language development is characterized by predictable changes in the words children produce and the complexity of their utterances. In infants these changes could reflect increasing linguistic expertise or cognitive maturation and development. To disentangle these factors, we compared the acquisition of English in internationally-adopted preschoolers and internationallyadopted infants. Parental reports and speech samples were collected for one year. Both groups showed the qualitative shifts that characterize first-language acquisition. Initially, they produced single-word utterances consisting mostly of nouns and social words. The appearance of verbs, adjectives and multiword utterances was predicted by vocabulary size in both groups.Preschoolers did learn some words at an earlier stage than infants, specifically words referring to the past or future and adjectives describing behavior and internal states. These findings suggest that cognitive development plays little role in the shift from referential terms to predicates but may constrain children's ability to learn some abstract words.

Language development is characterized by predictable shifts in the words that children learn and the complexity of their utterances. Because language acquisition typically occurs simultaneously with cognitive development and maturation, it is difficult to determine the causes of these shifts. We explored how acquisition precedes in the absence of possible cognitive or maturational roadblocks, by examining the acquisition of English in internationally-adopted preschoolers. Like infants, and unlike other L2 learners, these children acquire a language from child-directed speech in the home, without access to bilingual informants. Parental reports (CDI-2) and speech samples were collected from 14 preschoolers, 3 to 18 months after they were adopted from China. These children made rapid progress in acquiring English and showed the same developmental patterns as monolingual infants (matched for vocabulary size). Early on, their lexicons were dominated by nouns, their utterances were short, and function morphemes were almost entirely absent. Children at later stages of development had more diverse lexicons and produced longer utterances with more closed-class morphemes.

To explore early language acquisition in internationally adopted preschoolers, we collected parental reports (CDI-2) and speech samples from 14 children adopted from China between the ages of 2 years, 7 months and 5 years, 1 month. Their lexical and syntactic development was qualitatively similar to infants acquiring English as a first language: nouns and social words dominated early vocabularies; verbs and closed-class items became more frequent as vocabulary size increased; and lexical and syntactic development were tightly correlated. This research has several implications for clinicians. First, it demonstrates that parental reports provide valid information during the first year after adoption and could be useful in identifying preschool children in need of further assessment. Nine to 15 months after arrival many children reached the ceiling of the CDI-2, suggesting that this instrument has limited utility after the first year. Finally, the rapid lexical and syntactic growth of these children suggests that many of them may eventually catch up with their native-born peers.

Parents provide children with both genes (nature) and linguistic input (nurture). A growing body of research demonstrates that individual differences in children's language are correlated with differences in parental speech. Although this suggests a causal link between parental input and the pace of language development, these correlations could reflect effects of shared genes on language, rather than a causal link between input and outcome. We explored effects of maternal input on English vocabulary development in internationally-adopted (IA) children-a population with no genetic confound. IA preschoolers demonstrated some of the same correlations with input as in previous studies; specifically, measures of input quality were significantly correlated with vocabulary. However, IA infants did not demonstrate this pattern. Differences between the age groups may be related to the pace of acquisition; more rapid vocabulary development in the preschoolers suggests that access to, and children's ability to make use of input, may be a limiting factor for the infants.