Background This study aimed at exploring adolescents' attitudes to schizophrenia and the impact of an educational intervention on improving them, by employing a mixed methodology. Method A total of 1081 secondary‐school students were randomly allocated to a control and intervention condition. Stigma endorsement was assessed by a free association card and a questionnaire, before and 2 weeks after the intervention. Results The intervention yielded substantial changes in students' beliefs, attitudes and social distance levels as well as in their associations with the term ‘severe mental illness’. Conclusions Educational interventions can contribute substantially to preventing consolidation of unfavourable attitudes towards mental illness.