Young Latino children of immigrants typically speak primarily Spanish at home and are exposed to varying amounts of English. As a result, they often enter school with a wide range of proficiencies in each language. The current study investigated family background, language use at home and early childhood settings as predictors of Spanish and English language proficiencies among Latino dual language children (N = 228). Findings demonstrated divergent sets of predictors were associated with either Spanish or English proficiencies at kindergarten and second grade. Sociocultural variables (parent origin, gender, home language use, home literacy practices, and language use in early childhood settings) predicted children's Spanish proficiency, while socioeconomic variables (poverty, and maternal and paternal education) predicted children's English proficiency, with little to no overlap in these predictions. These results suggest that different supports are required for proficiency in Spanish and in English, highlighting the importance of sociocultural and socioeconomic factors.