Purpose: With the aim of contributing to the evidence base on school-based health promotion, the authors discuss the outcomes and processes of a European intervention project aiming to prevent obesity among children (4-16 years) and promote their health and well-being, titled "Shape Up: a school-community approach to influencing determinants of healthy and balanced growing up." Design/methodology/approach: Multiple case study research was carried out in five schools in five EU countries. Data sources included project documents, interviews, and observations. Narrative qualitative cross-case analysis was carried out following the single case analyses. Findings: The study showed that, if given sufficient guidance, pupils can act as agents of health-promoting changes on both school and local community level; they were involved in actions which improved school policies, provisions and affordances for healthier diet and regular physical activity. The study identified three forms of participation, each with a different level of pupil involvement and agency. Research limitations/implications: The study is qualitative, based on five single cases and cross-case analysis; this research design implies caution related to extensive non-contextualised generalisation of the findings. However, valuable implications for research and practice can be drawn, especially in relation to structural barriers for participatory health promotion. Originality/value: The paper is of value for researchers as well as practitioners in the field, particularly those interested in eco-social models of health, whole-school approaches to health promotion and pupil participation. The study's specific value is in the systematic qualitative cross-case analysis, which contributes to the research rigour and allows for situated generalisation. (Contains 2 notes and 1 table.)