The purpose of this study was to examine how classroom language contexts characterized by peer language skills and proportions of dual language learners (DLL) influenced English language development for DLL and non-DLL children. Participants were 2,131 children from 135 classrooms across preschool through Grade 3. Children were classified into fluent bilinguals (FBs, 12%), emergent bilinguals (EBs, 13%), and non-DLL (or English monolinguals [EMs], 75%). Over an academic year, FBs experienced similar growth in expressive vocabulary compared to EMs, both of which showed more growth than EBs, suggesting a bilingual advantage. Peer language skills and DLL composition were positively associated with DLLs' and non-DLLs' language development. Although having more EBs in the classroom lowered peer language skills, the overall influence that proportion of EBs had on children's language development remained positive. These findings shed light on the heterogeneity of DLLs and the complex social process of learning underlying linguistically and culturally diverse classrooms.