This study examined variations in the development of classroom aggression popularity norms, as well as the role of homeroom teachers' aggression beliefs and students' perceptions of teachers' support as predictors of such variations. To achieve this goal, a sample of 63 classrooms were assessed at four time points during a school year, in nine Colombian schools. Results indicated that, overall, classroom aggression popularity norms have a nonlinear trajectory with an increase that peaks at the end of the school year. Also, we found that teachers' aggression beliefs were concurrently associated with aggression popularity norms across time, and that teachers' support prevented the increase in these norms. These findings are discussed considering their practical implications for preventing aggression in the school context.