Abstract The main aim of the study was to investigate the role of individual and class justification of cyberbullying in predicting adolescents' cyberbullying perpetration over 6 months. The effects and moderating role of impulsivity, age, and gender in the hypothesized relationship between justification and cyberbullying were also tested. A sample of 750 Spanish adolescents (453 girls; mean age = 14.76; SD = 0.96) completed self-report measures at two time points during the same school year. Results from hierarchical linear modeling showed that individual-level cyberbullying justification at Time 1 significantly predicted higher levels of cyberbullying perpetration at Time 2 but only at low levels of impulsivity. Class-level justification significantly explained between-classes variability in cyberbullying perpetration at Time 2. Interestingly, this effect is moderated by age, indicating that the role of class justification was significant only for younger adolescents. Intervention efforts to prevent cyberbullying should center around the peer group at the class level and start during early adolescence.