Purpose: The purpose of this paper is to evaluate the health-promoting and stigma-reducing effect of the German school-based programme "Crazy? So what!". Design/methodology/approach: A quasi-experimental longitudinal control-study was carried out with assessments one week prior to the school programme, immediately after it and three months later. A total of 210 Year 9 and 10 students (aged 13-18 years) were surveyed in four schools in Saxony, Germany. Data analysis was done descriptively based on frequency distributions. Random effects regression models for unbalanced panel data were used to estimate the change of the outcome variables over time. Findings: At baseline, only 5.2 per cent of the intervention group would talk with their teacher about a mental health problem. Immediately after the programme, this number increased to 10.6 per cent and after three months to 17.9 per cent. There was also a positive, short-term effect on students' social distance, i.e. an increase in positive attitudes towards those with a mental illness, but this was not sustained over time. By contrast, self-efficacy proved resistant to change. Originality/value: This school programme is successful in that the "experts on their own behalf" (young people, who have gone through mental illness) were able to encourage and reassure others on how to face a mental health crisis with more confidence, which also contributes to strengthening students' resilience. The results of this study indicate the importance of sensitising children and youth, but also teachers and other adults to mental health. (Contains 3 tables, 2 figures and 2 notes.)