Esther Mertens

| 179 General Discussion were associated with weaker effect sizes (e.g., Emotion regulation, Discussions). This finding suggests opportunities to improve intervention effectiveness. However, optimizing interventions is complex as components’ effectiveness could depend on characteristics of the context and of the population. In sum, universal school-based interventions generally show small positive effects in the intra- and interpersonal domain, which is to be expected. These intervention effects appear dependent on intervention dosage and students’ personality traits. Nevertheless, the small intervention effects indicate that there is potential to improve the effectiveness of universal school-based interventions. 7