Adolescent students with high levels of antisocial behavior are at increased risk for future psychosocial problems and can be expected to be especially vulnerable to negative peer influence. This study therefore examined whether higher risk students are more susceptible than lower risk students to classroom peer influence on aggression. Analyses were based on anonymous self-reports from 792 students in 55 classrooms at four data collection points that span the beginning (T1) to the end (T4) of Grade 7. The mean age at T1 was 13.12 years (SD = 0.48 years) and 52.7% of the participants were boys. Students' risk status was assessed using a norm-based cutoff score from a standardized screening instrument. Multilevel analyses revealed that the aggression scores of higher risk students showed larger increases than those of other adolescents and that this difference was dependent on higher aggression levels among classmates. These results suggest that higher risk students may be particularly vulnerable to high levels of aggression in classrooms, whereas low levels of aggression in classrooms may be protective.