The authors examine endogenous peer effects, which occur when a student's behavior or outcome is a function of the behavior or outcome of his or her peer group. Endogenous peer effects have important implications for educational policies such as busing, school choice and tracking. In this study, the authors quantitatively review the literature on endogenous peer effects through the use of meta-analytic methods. They find a significant and positive endogenous peer effect. It appears to be a genuine empirical effect but is dependent on the measure of educational outcomes, the peer group, publication status, and publication year.