Abstract Issue/problem Schools constitute a key arena for promoting mental wellbeing among children and adolescents, and the Finnish welfare state has many beneficial structures in place for promoting mental wellbeing in schools. However, as mental health problems are prevalent, the need to advance this work is vital, ideally applying a holistic approach focusing on school-family interaction. Description of the problem The Finnish CONSENSUS project (2021-2025) focuses on the development of new practices and collaboration models in mental wellbeing promotion, targeting pupils in 13 primary schools in the Ostrobothnia region. The project answers question such as: What focal areas are prioritized by stakeholders in the development of mental wellbeing promotion in schools? How do participatory principles contribute to the development process and related outcomes? Results In 2024, a synthesis of previous project results (interviews, focus groups and longitudinal survey data collected among pupils, school personnel, school health care services and parents) was generated. The synthesis encompasses 20 possible priority areas to focus on in the development of mental well-being promotion actions, which are ranked by stakeholder representatives utilizing Delphi methods. Some pinpointed priority areas are implemented and evaluated in collaboration with self-selected schools during the academic year 2024-2025. Lessons Results highlight priorities in the development of mental wellbeing promotion in Finnish primary schools and describe focal areas being piloted, also illustrating opportunities and challenges when implementing participatory principles in action research projects. Key messages • Project results highlight prioritized areas in the development of mental wellbeing promotion in Finnish schools, as well as new initiatives currently being piloted. • The project approach emphasising participatory principles provides lessons for other initiatives focusing on mental wellbeing promotion development in schools.