This study examines the association between classroom characteristics and teacher-student agreement in perceptions of students' classroom peer networks. Social network, peer nomination, and observational data were collected from a sample of second through fourth grade teachers (N = 33) and students (N = 669) in 33 classrooms across five high-poverty urban schools. Results demonstrate that variation in teacher-student agreement on the structure of students' peer networks can be explained, in part, by developmental factors and classroom characteristics. Developmental increases in network density partially mediated the positive relationship between grade level and teacher-student agreement. Larger class sizes and higher levels of normative aggressive behavior resulted in lower levels of teacher-student agreement. Teachers' levels of classroom organization had mixed influences, with behavior management negatively predicting agreement, and productivity positively predicting agreement. These results underscore the importance of the classroom context in shaping teacher and student perceptions of peer networks.