Objectives: Increased recognition of the need for health education in schools has seen advances in health literacy in recent years. Most of these have focussed on physical health, whereas education about mental health is generally lacking and focussed on tackling stigma rather than promoting good mental health. This study evaluated a pilot intervention designed to improve young people's understanding of good mental health as a key aspect of wellbeing and explored their perceptions of health and wellbeing. Methods: A total of 218 13-year-olds participated in an interactive workshop about healthy eating, physical activity and mental health. Young people's understanding and perceptions were assessed through anonymous questionnaires at the start and end of the workshop. Common themes were identified and differences pre- and post-workshop and between girls and boys were analysed. Results: Nearly all young people (100% before, 97% after) perceived being healthy to mean being physically healthy. A minority (8%) also considered mental health to be a component of general health, which increased to 12% after the workshop. Understandings of mental health broadened after the workshop. Interestingly, many mentioned physical health when asked to describe mental health, both before and after the workshop. Girls' and boys' responses were similar except for more girls including social relationships in their descriptions of mental health. Conclusion: In this study, we have discovered much about how young people perceive health in general and mental health. Such information is useful for targeting future interventions. Students' understanding of mental health and its importance to wellbeing can be improved through short combined health interventions.