Norms have been suggested as important characteristics of the social-ecological context for defending victimized peers, but little is known about the contribution of student perceived injunctive norms (regarding the appropriateness of defending) imposed by peers and teachers. To investigate the role of these norms in defending, a sample of 751 early adolescents (51% female; Mage at Time 1:13 years) was assessed at two time points. Defending, as measured by peer- and self-ratings, decreased slightly over a six-month timespan. Three-level models (with time, students, and classrooms as the levels) indicated that both individual- and classroom-level perceived peer injunctive norms (but not teacher injunctive norms) had positive effects on defending over time regardless of the source of the information on defending (peers or self). These findings support programs that encourage defending through peer norms.