Bilingual children sometimes respond to their interlocutors using a different language than the one in which they were addressed. These language choices, their concurrent correlates, and relations to subsequent language growth were examined in 91 Spanish-English bilingual children (44 girls, 47 boys). Children's language choices were assessed at 30 months, and their English and Spanish productive vocabularies and receptive language skills were examined at the ages of 30, 36, and 42 months. Children's language choices were concurrently related to English and Spanish productive and receptive language scores and to mothers' English and Spanish proficiency levels. Longitudinal multi-level modeling analyses indicated that children's language choices at 30 months were uniquely related to language growth on measures of English and Spanish productive vocabulary and Spanish receptive language, when controlling for language expo sure. These findings suggest that language use plays a causal role in language development. The findings of this study have implications for the maintenance of heritage languages in the U.S. and for the development of children's English language skills. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection