The purpose of this sequential explanatory mixed methods study was to investigate teacher and peer support for young adolescents’ academic motivation, classroom engagement, and school belonging within one large, urban, ethnically diverse middle school. In the initial quantitative phase, associations among aspects of teacher support (autonomy, structure, and involvement), peer support (academic and emotional), and adjustment (motivation, engagement, and belonging) were examined using student surveys (N = 209, 61% females). In the follow-up qualitative phase, participants elaborated on the ways teachers and peers support young adolescents’ adjustment during individual interviews (N = 18 students, 5 teachers, and 1 administrator). Results indicate teacher and peer support are academic and social in nature and have unique implications for supporting motivation, engagement, and belonging in middle school. By utilizing a mixed methods design and adopting a multidimensional perspective of classroom-based support, our findings provide a comprehensive understanding of the role of teacher and peer support on student adjustment. An implication for educators is for them to understand the ways teacher and peer support may help meet young adolescents’ needs and promote their academic motivation, classroom engagement, and school belonging. Findings may inform middle level educational research and practice, especially in urban, ethnically diverse middle level schools.