With its compensatory mandate, the school is essential for health-promoting interventions. There are evaluated programs available that prevent mental problems, mental illnesses and various risk behaviours. However, there is a dearth of evaluated interventions designed to promote mental well-being in adolescents, which are adapted for upper secondary school. It was against this background that the development and evaluation of the Solution-focused Intervention for Mental health (SIM) began in 2018. This presentation will briefly overview the intervention, its components, design and results from feasibility studies. As an intervention programme, SIM consists of group-based coaching that starts from the core components and indicators of mental well-being and enjoying school. Thus, the intervention is based on a normative model of mental well-being; however, the dialogue conducted during the nine two-hour weekly group sessions is based on the solution-focused approach and its techniques. Specially trained teachers facilitating the content and process during group sessions lead SIM. The SIM programme is manual-based and designed to help students discover, explore, practice and develop existing personal resources in order to strengthen hedonic and eudemonic well-being. The teacher uses solution-focused coaching techniques to encourage the students to practise and discover how to utilise their existing resources. By focusing on what works small steps can be taken towards a desired future using indicators of well-being and solution-focused techniques. SIM has so far been tested in feasibility studies in 2019 (n∼140), 2021 (n∼200) and 2023 (n∼50). Results from focus group interviews, session scales ratings and pairwise testing of changes in well-being after compared to before interventions show promising results with increased well-being and total effect sizes ranging from Coheńs d of 0.19 to 0.59. SIM is now ready to be properly evaluated in a randomised controlled trial.