Background: School bullying is a wide-spread problem with severe consequences for victims, bullies and bystanders. Schools are strongly encouraged to implement both schoolwide, preventive interventions and reactive measures to handle existing bullying situations. In the Dutch implementation of the KiVa anti-bullying programme, pervasive-bullying situations are addressed according to the support group approach. The support group approach is widely used for addressing bullying situations, but little is known about its effectiveness. Purpose: We investigated the effectiveness of the support group approach in reducing victimisation, increasing defending and improving the victim's well-being over the course of a school year, over and beyond of the effects of the universal KiVa intervention. Programme description: The support group approach is a non-punitive, problem-solving strategy to address pervasive-bullying situations. In this intervention, trained teachers form a support group that consists of 6-8 children, including the bullies and their assistants, defenders or friends of the victim and prosocial classmates. The purpose of the support group is to create mutual concern for the well-being of the victim and to trigger the bullies' willingness to alter their behaviour. Sample: We used data from 66 Dutch elementary schools that participated in the KiVa intervention study. Data were collected in October 2012 and 2013, and May 2013 and 2014. The sample used in the analyses consisted of 38 victims for whom a support group intervention was organised (44.7% boy, M[subscript age] = 9.24; SD[subscript age] = 1.20). Design and method: To get insight into the effects above and beyond those of the KiVa programme itself, victims with a support group (N = 38) were matched to similar victims without a support group (N = 571). Statistical analyses were undertaken to examine whether the changes in victimisation, defending and well-being at school differed between the two groups. Result: Victims reported positive effects of the support group approach in reducing victimisation in the short term, but this decrease in victimisation was not lasting over the course of a school year. The intervention also did not improve the victims' well-being at school in the longer term. Victims with a support group, however, were found to have more defenders at the end of the school year than victims without a support group. Conclusion: The effectiveness of the support group approach in tackling bullying situations appears to fade over time. The findings of this study illustrate that for future evaluations of anti-bullying interventions it is essential to investigate longer term effects.