The aim of the current study was to examine whether moral disengagement and defender self-efficacy at individual level and collective efficacy to stop peer aggression at classroom level were associated with defending and reinforcing in school bullying situations in late childhood. Self-reported survey data were collected from 1060 Swedish students from 70 classrooms in 29 schools. Multilevel analysis found that greater defender self-efficacy at individual level and collective efficacy to stop peer aggression at classroom level were associated with greater defending. We also found that greater moral disengagement and less (but very weakly) defender self-efficacy at individual level and less collective efficacy to stop peer aggression at classroom level were associated with greater reinforcing. The positive relationship between moral disengagement and reinforcing and the negative relationship between defender self-efficacy and reinforcing were less strong in classroom high in collective efficacy to stop aggression.