The aims of the present meta-analysis were to (1) examine long-term effects of universal secondary school-based interventions on a broad range of competencies and problems and (2) analyze which intervention components were related to stronger or weaker intervention effects at follow-up. Fifty-four studies of controlled evaluations (283 effect sizes) reporting on 52 unique interventions were included. Long-term intervention effects were significant but small; effect sizes ranged from .08 to .23 in the intrapersonal domain (i.e., subjective psychological functioning) and from .10 to .19 in the interpersonal domain (i.e., social functioning). Intervention components were generally related to effects on specific outcomes. Some components (e.g., group discussions) were even related to both stronger and weaker effects depending on the assessed outcome. Moreover, components associated with long-term effects differed from those associated with short-term effects. Our findings underscore the importance of carefully selecting components to foster long-term development on specific outcomes.
PROSPERO registration number: CRD42019137981.