Nutrition education at school can contribute to developing healthy nutritional behaviours in schoolchildren. This paper critically reflects on how participatory action research (PAR) empowered university researchers and a school community to co-develop a school-based nutrition education programme (SBNEP) that promotes healthy nutritional behaviours in basic-level schoolchildren (Grades 1-8). This study followed PAR as the methodological approach, where university researchers collaborated with the school stakeholders, also called 'co-researchers', to co-develop a SBNEP. This study was conducted in a public school located in the Chitwan district of Nepal from June 2018 to August 2022. The study involved basic-level schoolteachers, fourth to eighth-grade students and their parents/guardians, school leaders, and the PAR committee members as the co-researchers. The study used in-depth interviews, focus groups, participant observation, informal talks, and bridging-the-gap workshop methods. The interpretive phenomenological method was used to explain the meaning of the data. The findings of the study reflect that exploring the needs for good nutritional behaviours, prioritising them, and co-designing the SBNEP utilising the PAR methodology is a time-consuming project since it demands prolonged fieldwork, self-motivation, commitment, action with critical reflection (praxis), dialogic relation, and negotiation skills from both researchers and co-researchers. The study recommends that basic-level schoolteachers and researchers consider applying SBNEP using a participatory framework for transformational change in students' nutritional behaviours.