Introduction: Marked gender differences have been identified in cyberbullying perpetration and victimization in adolescence. Age and phenotypic traits, including impulsivity and problematic internet use may mediate the association between gender and cyberbullying intervention outcomes. This study thus aimed to explore gender differences and the potential mediating role of age, impulsivity and problematic internet use regarding the outcomes of an elementary school cyberbullying program. Methods: The peer-led STAnD project shapes students' attitudes towards cyberbullying, and promotes help-seeking behaviors. Baseline sample consisted of 933 respondents (51.3% females, mean age = 11.25, sd = 1.64), and after a 42.55% drop-out, 536 remained in the sample for 6-month follow-up. Four primary outcome measures represented protective factors against cyberbullying. Results: Three of the intervention outcomes – change in 1) helpline knowledge, 2) empathy towards the victims of cyberbullying, and 3) risk perception regarding online hazards - were best predicted by gender. A gender-specific path analysis model indicated that higher amount of time spent online might put a barrier to changes in risk awareness among females and in help-seeking willingness among males. Conclusions: Future cyberbullying programs may design separate interventions for adolescent boys and girls with different emphasis placed on empathy training, or the barriers to help-seeking.