The unique relation of language use (i.e., output) to language growth was investigated for forty-seven 30-month-old Spanish-English bilingual children (27 girls, 20 boys) whose choices of which language to speak resulted in their levels of English output differing from their levels of English input. English expressive vocabularies and receptive language skills were assessed at 30, 36, and 42 months. Longitudinal multilevel modeling indicated an effect of output on expressive vocabulary growth only. The finding that output specifically benefits the development of expressive language skill has implications for understanding effects of language use on language skill in monolingual and bilingual development, and potentially, for understanding consequences of cultural differences in how much children are expected to talk in conversation with adults.