Purpose: Although implementation fidelity is an important component in the evaluation of school health promotion programs, it assumes that teaching is the most relevant teacher role. To understand the social context of program implementation, a qualitative study was undertaken with the aim of identifying the schoolteacher's role in implementing the objectives of the Kahnawake Schools Diabetes Prevention Project (KSDPP), a locally governed Kanienke:haka (Mohawk) community-based diabetes prevention program. Design/methodology/approach: Prospective semi-structured interviews were conducted cross-sectionally with 30 teachers, two administrators and one physical education teacher across four intervention years. Interviews were analysed retrospectively using qualitative thematic analysis. Findings: In implementing KSDPP objectives teachers adopted, to varying degrees, the roles of teaching the health education curriculum, enforcing the school nutrition policy, role modelling healthy lifestyles, and encouraging healthy lifestyles. Taken together, these roles point to a high-order role of teachers taking responsibility for enabling healthy lifestyles in their children, which is congruent with a wholistic approach to health. Study findings suggest that children in different classrooms were exposed to a different intervention dose based on the extent to which teachers applied each role. Research limitations/implications: The findings suggest that the current conceptualisation of implementation fidelity should be expanded to account for the influence of the social context (i.e. teachers' roles) on the implementation of health promotion program objectives. Originality/value: Consistent with an ecological approach to intervention, teachers would benefit from interventions that predispose, enable, and reinforce their capacity to adopt and apply health promotion roles. (Contains 1 figure and 1 table.)