This paper discusses the findings of a multiple case study of a European health promotion project - ‘Shape Up – a school-community approach to influencing determinants of a healthy and balanced growing up’. The project sought to develop children’s capacity to critically explore and act to improve health-related conditions at school and in the community. The aim of the study is to explore learning outcomes, defined as changes in pupils’ action competence, of the Shape Up project. Further, the study addresses the interplay between the project’s methodology and contextual factors related to its implementation and its impact on learning outcomes. Case study research was conducted in five schools in five different countries. Data were generated through document analysis, interviews and observations. A cross-case analysis was conducted, inspired by the Context-Mechanism-Outcome analytical framework proposed by Pawson and Tilley (1997). Changes related to pupils’ knowledge, skills, visions, critical thinking and decision making, experience with taking action and a realization that they can change things stand out as essential for the pupils’ developing sense of action competence. Two different implementation forms of the project’s methodological approach were identified across the five cases, both conducive to changes in pupils’ action competence.