Purpose - Implementing health promotion programmes in schools is key to improving children's health and well-being but difficulties in achieving expected results are often reported in the research literature. Discrepancies between expected and achieved outcomes can originate from differences in contexts. Understanding how interactions between contexts and programmes generate variable outcomes is, therefore, critical. The purpose of this paper is to explore the outputs of a programme implemented in different school contexts. The focus is to pinpoint outputs, understand the involvement of combinations of contextual factors and identify recurrences in these combinations. Design/methodology/approach - This retrospective study covers a period from 2006 to 2016. Data collection includes two sets of data in eight high schools in the Rhone-Alpes Region in France: written documents and interviews with school staff. Realist evaluation is used to attempt to pinpoint outputs and relating contextual factors. Findings - Results highlight the limited outputs of the programme. Differences between schools appear to originate from existing school policy prior to participation, existence of a project team, identification of the issue as priority and staff turnover. Analysis of contextual factors led to considering the implementation process as enabling health capacity building and enhanced the capacity of settings and communities to promote health. Originality/value - Previous research suggests that top-down implementation of a standard programme is not an efficient strategy for all schools to engage in the development of suitable health promotion policies. A potential way forward is to base support for the local development of health promotion in schools on a better understanding of the contexts in which implementation occurs.