Using a unique longitudinal dataset covering all Florida public school students in grades 3–10 over a five-year period, we analyze the impact of classroom peers on individual student performance. Unlike many previous data sets used to study peer effects in education, our data allow us to identify each member of a given student's classroom peer group in elementary, middle and high school as well as the classroom teacher responsible for instruction. As a result, we can control for individual student fixed effects simultaneously with individual teacher fixed effects, thereby alleviating biases due to endogenous assignment of both peers and teachers, including some dynamic aspects of such assignments. We find some sizable, significant peer effects within nonlinear models, but not with linear specifications. We find peer effects depend on a student's own ability and on the ability of the peers under consideration. Peer effects tend to be smaller when teacher fixed effects are included, a result that suggests co-movement of peer and teacher quality within a student over time. We also find that peer effects tend to be stronger at the classroom level than the grade level.