Frequent exposure to victimization by peers is related to greater psychological problems. It is often assumed that peer victimization is associated with fewer psychological problems in classrooms where defending victims of bullying is common (i.e., a norm). The few studies testing this claim have been cross-sectional and have produced mixed findings. The current preregistered study examined whether the prospective link between victimization and psychological adjustment (i.e., depressive symptoms and self-esteem) was moderated by classroom defending norms. Moreover, we aimed to explain why defending norms may have either beneficial or adverse effects on victims' adjustment, by focusing on two cognitive processes: victims' causal attributions and social comparisons. Three waves of data were collected among 3,470 Finnish fourth- to ninth-grade students from 227 classrooms (M[subscript age] = 13.04, 50.1% girls). Multilevel regression analyses showed that nonvictimized youth benefited from high defending norms, whereas victims' psychological adjustment did not vary as a function of defending norms. Therefore, no mediation analyses were conducted. Nonpreregistered additional analyses indicated that stable victims had greater psychological problems and higher self-blame over time in classrooms with higher defending norms. Thus, even though the majority of students seem to profit from defending norms, this might not be true for those who most urgently need help.