Background: With the increase of cyberbullying, several intervention programmes have been created that aim at reducing cyber-victimisation and perpetration. Objective: Our study presents the effects of the STAnD anti-cyberbullying programme with peer-education both on the short and the long run among lower and upper primary school students, with a focus on the participants’ cyberbullying roles. Method: The sample comprised of 536 students who participated in the intervention programme, involving 36% lower and 64% upper primary school students. Participants were measured by a self-reported questionnaire before and right after the programme, then six months later. Results: The main effect of the STAnD programme was a positive change in the participants’ willingness to engage in help-seeking and their active-defending reaction, although this effect decreased after six months. The changes were larger among lower primary school students compared to upper primary school participants. Conclusion: Our results imply that long-lasting and intensive health promotion programmes are necessary to reach a long-term intervention effect. Anti-cyberbullying programmes should take into consideration participants’ involvement and roles in cyberbullying. As our study was a non-randomised uncontrolled study design, thus interpretation of the effectiveness of the programme is limited.