BackgroundLack of formal education is an important social determinant of health inequality and represents a public health problem. School dropout is particularly common in vocational education; however few prevention programs targeting dropout in the vocational school setting have been evaluated. The purpose of the present study was to test the effect on school dropout of a settings-based intervention program (named Shaping the Social) that targeted the school organization in order to create social and supportive learning environments.MethodsA non-randomized controlled design including four large intervention schools and six matched-control schools was used. The target population was students in technical and agricultural vocational education, which is provided to students from age 16. Students were enrolled at school start. Register-based data (n = 10,190) was used to assess the effect on school dropout during a 2-year period. Odds ratios (OR) and 95% confidence intervals (CI) were calculated in logistic regression models, adjusting for age, sex, ethnicity, parental income, prior school dropout and type of basic course. Student survey (n = 2396) at 10-week follow-up was used to examine wellbeing at school (four subscales: school connectedness, student support, teacher relatedness, and valuing the profession) which was the hypothesized proximal intervention effect. As a secondary aim, we examined how the student wellbeing factors were associated with school dropout, independently of the intervention, and we explored whether the student wellbeing factors were potential mediators.ResultsThe present study showed an intervention effect on school dropout with dropout rates lower in intervention schools (36%) than control schools (40%) (OR = 0.86, 95% CI: 0.74, 0.99). We had no attrition on the dropout outcome. School connectedness mediated the intervention effect; no significant mediation effects were found for student support, teacher relatedness, and valuing the profession. Independently of the intervention, each student wellbeing factor prevented dropout.ConclusionsFindings from this study suggest that a comprehensive, multicomponent school-based intervention could prevent dropout from vocational education by promoting school connectedness; nevertheless, the dropout rate remained high. Our results point to the need to explore how to further improve the wellbeing at school among young people in vocational education.Trials registrationISRCTN, ISRCTN57822968. Registered 16 January 2013 (retrospective registered).