Background <p>Self-harm is common among adolescents and recognised as a significant public health issue. This study aimed to explore the perspectives of young people and school staff about how schools should respond to self-harm and subsequently develop principles of practice.</p> Methods <p>Seven focus groups were carried out with school staff and young people. Qualitative data were thematically analysed using the Framework Method to generate themes [<CitationRef CitationID="CR1">1</CitationRef>, <CitationRef CitationID="CR2">2</CitationRef>]. The findings were translated into actionable items by applying the Implementation in Schools Framework [<CitationRef CitationID="CR3">3</CitationRef>].</p> Results <p>Staff and students had overlapping views about how schools should address self-harm. These were captured in three themes (1) Understanding the nature and scope of self-harm in schools, (2) Building whole school capacity to respond to self-harm, (3) Creating a supportive school environment. Principles of practice were generated to guide schools in their approach to self-harm.</p> Conclusion <p>For many young people, schools are a key setting for early intervention in self-harm; however, staff often feel ill-equipped to respond and clear guidance is lacking. This study has developed evidence-informed principles of practice for UK schools, drawing on the perspectives of staff and young people to inform a whole school approach.</p>