Participants were 360 (52.2% male) ethnically diverse and academically at-risk first-grade children attending one of three school districts in southeast and central Texas. Using latent variable structural equation modeling, we tested a theoretical model positing that the quality of the teacher-student relationship in first grade predicts children's peer acceptance the following year, controlling for children's previous externalizing problems and peer acceptance. We also expected that children's classroom engagement would mediate the effect of teacher-student relationship quality on peer acceptance. The hypothesized model provided a good fit to the data. Engagement fully mediated the effect of teacher support on subsequent peer acceptance. Neither ethnicity nor gender moderated the mediation findings.