Esther Mertens

| 157 General Discussion interpersonal domain). Interventions are often somewhat adjusted and implemented in different contexts or with different types of participants than for which the interventions were intended and evaluated (Durlak & DuPre, 2008). Given that the extent to which intervention effects can be generalized is often limited (Rowe & Trickett, 2018), schools and professionals are advised to monitor participants’ change, for instance, by asking participants, teachers, or parents on a regular basis to complete a questionnaire. Monitoring progress enables schools and professionals to evaluate whether the intervention works in that specific context, population, and domain, or whether a different approach needs to be adopted (Flay et al., 2005). Conclusion Overall, universal school-based interventions showed small positive effects in enhancing students’ competencies and preventing the development of problems in the intrapersonal and interpersonal domain. More specifically, R&W seems to hold some promise to target prevocational students. Given that the effectiveness of an intervention depends on characteristics of the context (e.g., intervention dosage) as well as of students (e.g., personality traits), small intervention effects can be expected in universal school-based interventions which are often implemented in a broad context and in a broad population. Nevertheless, it remains important to strive towards optimization of universal interventions. My meta-analysis indicated opportunities to improve these interventions as components related to stronger intervention effects were not necessarily often implemented and some commonly implemented components were associated with weaker intervention effects. Taken together, the present dissertation showed that overall universal school-based interventions are somewhat effective in fostering students’ development in the intra- and interpersonal domains and indicated opportunities to further improve the effectiveness of these interventions. 7