Research with monolingual children has shown that early efficiency in real-time word recognition predicts later language and cognitive outcomes. In parallel research with young bilingual children, processing ability and vocabulary size are closely related within each language, although not across the two languages. For children in dual-language environments, one source of variation in patterns of language learning is differences in the degree to which they are exposed to each of their languages. In a longitudinal study of Spanish/English bilingual children observed at 30 and 36 months, we asked whether the relative amount of exposure to Spanish vs. English in daily interactions predicts children's relative efficiency in real-time language processing in each language. Moreover, to what extent does early exposure and speed of lexical comprehension predict later expressive and receptive vocabulary outcomes in Spanish vs. English? Results suggest that processing skill and language experience each promote vocabulary development, but also that experience with a particular language provides opportunities for practice in real-time comprehension in that language, sharpening processing skills that are critical for learning.