Background: The Health-Promoting School (HPS) framework offers a comprehensive approach to promoting health in schools. Aragon's HPS network is a local organisation which has identified the need for closer cooperation between the education and health sectors as the main challenge facing its programme. Objectives: Previous studies from countries implementing HPS approaches have identified various outcomes and challenges. However, there is insufficient evidence to identify potential barriers to HPS implementation in Spain. This study therefore set out to explore these issues within the context of the HPS network in Aragon. Method: Three focus groups were held in different cities (Zaragoza, Huesca and Teruel) between April and May 2020. The total sample comprised 18 adults (M = 45.21; SD = 12.61), 60% of whom were men. Eleven participants were HPS stakeholders (i.e. teachers, HPS coordinators) and seven were external collaborators (e.g. university professors, researchers). Results: The main barriers identified were the excessive workload for professionals involved in the network, limitations imposed by contextual factors such as lack of teacher and family involvement, and lack of supervision and communication within the HPS network. Strengthening collaboration with work in other settings, the provision of continuing education for teaching staff and more systematic evaluation were identified as potential ways forward. Conclusion: Using the principles identified in this paper, Aragon's HPS network should be further developed to enhance effective implementation and improve sustainability.