The extant literature includes conflicting assertions regarding the influence of bilingualism on the rate of language development. The present study compared the language development of equivalently high-SES samples of bilingually and monolingually developing children from 1;10 to 2;6. The monolingually developing children were significantly more advanced than the bilingually developing children on measures of both vocabulary and grammar in single language comparisons, but they were comparable on a measure of total vocabulary. Within the bilingually developing sample, all measures of vocabulary and grammar were related to the relative amount of input in that language. Implications for theories of language acquisition and for understanding bilingual development are discussed.

Purpose Vocabulary assessment holds promise as a way to identify young bilingual children at risk for language delay. This study compares 2 measures of vocabulary in a group of young Spanish–English bilingual children to a single-language measure used with monolingual children. Method Total vocabulary and conceptual vocabulary were used to measure mean vocabulary size and growth in 47 Spanish–English bilingually developing children from 22 to 30 months of age based on results from the MacArthur–Bates Communicative Development Inventory (CDI; Fenson et al., 1993) and the Inventario del Desarrollo de Habilidades Comunicativas (Jackson-Maldonado et al., 2003). Bilingual children’s scores of total vocabulary and conceptual vocabulary were compared with CDI scores for a control group of 56 monolingual children. Results The total vocabulary measure resulted in mean vocabulary scores and average rate of growth similar to monolingual growth, whereas conceptual vocabulary scores were significantly smaller and grew at a slower rate than total vocabulary scores. Total vocabulary identified the same proportion of bilingual children below the 25th percentile on monolingual norms as the CDI did for monolingual children. Conclusion These results support the use of total vocabulary as a means of assessing early language development in young bilingual Spanish–English speaking children.

The relation of phonological memory to language experience and development was investigated in 41 Spanish-English bilingual first language learners. The children’s relative exposure to English and Spanish and phonological memory for English-like and Spanish-like nonwords were assessed at 22 months; their productive vocabulary and grammar in both languages were assessed at 25 months. Phonological memory for English- and Spanish-like nonwords were highly correlated, and each was related to vocabulary and grammar in both languages, suggesting a language-general component to phonological memory skill. In addition, there was evidence of language-specific benefits of language exposure to phonological memory skill and of language-specific benefits of phonological memory skill to language development.

Two studies test the hypotheses that individual differences in phonological memory among children younger than two years can be assessed using a non-word repetition task (NWR) and that these differences are related to the children's rates of vocabulary development. NWR accuracy, real word repetition accuracy and productive vocabulary were assessed in 15 children between 1 ; 9 and 2 ; 0 in Study 1 and in 21 children between 1 ; 8 and 2 ; 0 in Study 2. In both studies, NWR accuracy was significantly related to vocabulary percentile and, furthermore, uniquely accounted for a substantial portion of the variance in vocabulary when real word repetition accuracy was held constant. The findings establish NWR as a valid measure of phonological memory in very young children, and they open the door for further studies of the role of phonological memory in early word learning.

Effects of child and environmental factors in moderating the course of bilingual development were investigated using longitudinal data, from age 2.5 to 5 years, on 126 U.S.-born children with early exposure to Spanish and English. Multilevel models of Spanish and English expressive vocabulary identified children's phonological memory ability as a significant predictor of both outcomes, while also replicating the effect of the relative amount of language exposure. In addition, nonverbal IQ was a significant predictor of English vocabulary; birth order and maternal education in Spanish were significant predictors of Spanish vocabulary. These findings expand our understanding of the sources of the wide heterogeneity in bilingual development and of the requirements that language acquisition makes of learners and their environments.