Participatory systems approaches are suggested to address the complex drivers of adolescent health but have not been applied or evaluated in a vocational school setting. This study investigated the implementation of a participatory systems approach to health promotion and its potential for driving system-level changes in vocational schools. We used quantitative data to assess implementation fidelity (reach, recruitment, and dose) and outputs in terms of the potential for system-level changes (engagement, knowledge, and leverage points). Qualitative data examined contextual factors (participant responsiveness, and school and municipal contexts) as potential influences on implementation fidelity and outputs. The results showed that school, municipal, and community actors actively participated in systems mapping and in identifying actions targeting leverage points at various system levels. Engaged and knowledgeable community actors were found to be key in generating ideas targeting the deeper layers of the system, enhancing the potential for successful implementation and system-level change. Implementation fidelity and outputs varied across sites due to varying responsiveness and school and municipal contextual factors. In conclusion, participatory systems approaches in vocational schools are feasible, leading to action ideas with promising leverage points for health promotion. However, a flexible approach tailored to specific school and municipal contexts is needed.