Abstract Background The Dutch Healthy School Program (‘Programma Gezonde School’; HSP) is a whole school approach including education, stimulating physical and social environment, health services, and school health policies. Implementation support is offered by Healthy School Advisers employed at 25 regional Public Health Services (PHSs). To strengthen this professional support, this study aimed to map conditions for the degree of support offered by PHSs and received by schools. Methods The data collection plan was developed together with a Community of Practice. In 2021 and 2022, two rounds of semi-structured group interviews were conducted in 8 PHSs (N = 1-4 employees and ±3.5 hours in total per PHS). Interviews focused on the degree of support (intensity, quality, context-focus, position in PHS and region) and 24 contextual factors regarding: 1) Healthy School Advisers, 2) PHS organization, 3) collaboration with partners, and 4) broader context. Additional data were collected from public websites, year reports, and the Dutch registry of implementing HSP. Data were analyzed thematically in Nvivo. Preliminary results There is large variation in all aspects of support between PHSs. Main conditions for this variation are related to the PHS organization: its policy, internal support, capacity, and (long-term) allocated budget. Other key conditions are related to collaboration with partners: coordination, division of responsibilities, and communication structure. Prerequisites for all PHSs were cohesive adviser teams, the HSP, and national school health promotion focus. Conclusions In order to strengthen professional support for whole school health promotion implementation, it is essential to: 1) establish strong positioning and (long-term) resources in the organization, 2) establish clear coordination between Healthy School Advisers and partners supporting schools, 3) maintain cohesion among adviser teams, and 4) maintain and intensify national (school) health promotion policy. Key messages • Degree of ...