Although researchers often acknowledge the importance of linguistically rich interactions in the academic language development of emergent bilingual students, few studies have explicitly examined the role of linguistic peer support and the underlying structure of social relationships in the second language learning experiences and outcomes of immigrant adolescents in schooling contexts. This mixed methods study investigates the role of peers--including bilingual peers--in the development of oral academic English during adolescence. Using social network analysis, this study describes the unique contribution of peer linguistic resources to the oral Academic English Proficiency of 102 adolescent Spanish-speaking immigrant students. Findings show that having bilingual peers who collaborated on academic tasks with participants, in English or Spanish, contributed to academic English proficiency beyond individual predictors of second language acquisition (age, time in the United States, gender, and maternal education). Peer social network composition indexed the opportunities adolescent English learners encountered at school to learn and use academic English.