Background and Objective: School is a core setting for health promotion in children and adolescents. However, several large school-based health promotion programs fail to succeed, often because of a top-down approach. The aim of this study was therefore to explore involvement of students in the evaluation and implementation of a school-based, health promotion program in a vocational study program in a Norwegian upper secondary school. The program aimed to increase school-based physical activity, improve quality of the school meal, and the psychosocial school environment. Methods: The study had a participatory research design where students were involved in the knowledge development. A student competence group (SCG, n=8) collaborated with the researchers in the evaluation of implementation of the school- based health promotion program. Data were collected in three waves (spring 2021, autumn 2021, and spring 2022), the SCG met with the researchers twice per data collection. The empirical data for this study is based on a total of these six meetings. Results: The involvement of SCG was crucial for the ability to identify important topics for the data collection. The SCG influenced the study by contributing to the development of the interview guide for the qualitative study. Moreover, the SCG modified questions for the survey. The SCG contributed and nuanced the Interpretation of the quantitative and qualitative data. Conclusions: The study showed how participatory research can influence different stages of an evaluation and implementation process for health programs in school settings. The involvement of students in SCG provided wider perspectives and pointed out practical implications of the study. There is a need for further research to explore power dynamics and new methods of youth participation in public health research.