During adolescence, peer groups present an important venue for socializing school-related behaviors such as academic achievement and school engagement. While a significant body of research emphasizes the link between a youth's immediate peer group and academic outcomes, the current manuscript expands on this idea, proposing that, in addition to smaller peer groups, within each school exists a school-wide peer culture that is comprised of two components (a relational and a behavioral component), each of which is related to individual academic outcomes. The relational component describes the aggregate of students' perceptions of the quality of peer relationships within each school. The behavioral component is an aggregate representation of students' actual behaviors in regard to academic tasks. We used data from the 4-H Study of Positive Youth Development, which surveyed 1,718 5th grade students (45.9% male, 51.4% White, 17.8% Hispanic, 7.6% African American) in 30 schools, to explore the idea that, during adolescence, the relational and behavioral components of a school's peer culture are related to students' academic achievement and school engagement. Results suggested that above and beyond a variety of individual, familial, peer, and school characteristics that have previously been associated with academic outcomes, aspects of behavioral peer culture are associated with individual achievement while components of both relational and behavioral peer culture are related to school engagement. Implications for future research are discussed.