The aim of the present study was to examine to what extent classroom factors (i.e., classroom antibullying attitudes and behavioral norms) contributed to individual bullying, after controlling for individual difference characteristics. Participants were 2,547 early adolescents (M = 13.4 years, SD = 0.63) from 109 middle school classes. Self- and peer reports were used to answer the research questions. It was found that adolescents in classrooms that held permissive attitudes toward bullying were more likely to bully themselves, even after controlling for individual attitude, gender, social preference, and number of reciprocal friends. However, the association of classroom attitudes with individual bullying decreased substantially when classroom bullying behavior was taken into account. Our study suggests that the effects of classroom antibullying attitudes might be partly mediated by classroom behaviors. It implies that research that has not included classroom behavior might have overestimated the effects of classroom attitudes on bullying. (Contains 3 tables and 1 footnote.)