School-based programmes to reduce and prevent substance use in different age groups: What works for whom? Systematic review and meta-regression analysis

Background: Findings from systematic reviews and meta-analyses about the effectiveness of school-based programmes to prevent or reduce substance abuse are inconclusive. We hypothesise that in order to be effective, programmes have to be aligned with the developmental stages of the intended target group (childhood, early, middle, or late adolescence). The present study provides an overview of universal and targeted programmes, while distinguishing four age groups and examining which intervention characteristics are the effective components for the respective groups. Methods: Databases were searched for controlled studies of school-based programmes, evaluating their effectiveness on either smoking, alcohol or drug use. Multivariate meta-regression analysis was used to analyse the associations between effects and programme characteristics. Results: Our meta-analysis evaluates 288 programmes with a total of 436,180 participants. The findings support our hypothesis that specific aspects of the school-based programmes are effective in some developmental stages, but not for other age groups. The differences in effectiveness are systematically related to psychological and cognitive needs and capacities. Discussion: Our findings highlight the importance of considering a developmental perspective when designing and offering school-based prevention programmes. The various developmental stages offer different possibilities and opportunities for the reduction and prevention of substance use