Purpose: Contextual factors can influence the implementation of whole-school health promotion and compromise its impact among students. This study aimed to identify key (combinations of) contextual factors in the implementation of whole-school health promotion at Dutch primary, secondary and secondary vocational schools. Design/methodology/approach: Forty-three schools with either a high or low degree of implementation were selected. Data were collected prior to and during school visits using mixed methods, covering 36 contextual factors related to school employees, school organization, the national Health Promoting School program, socio-political environment, physical environment, implementation support, student population and COVID-19. Data were analyzed using Qualitative Comparative Analysis for primary and secondary schools and qualitative analysis for secondary vocational schools. Findings: Key combinations of conditions were (1) resources, (2) school climate, (3) implementation support, (4) identification as Health Promoting School, (5A) at primary schools: parental support and (5B) at secondary and secondary vocational schools: coordination and competencies. Often decisive to a high degree of implementation were the roles of principals and coordinators (as part of the school climate and coordination). Often decisive to a low degree of implementation were limited perspectives regarding prevention among employees (as part of the school climate). Identification as Health Promoting School and implementation support were mainly crucial when there were challenges in other key conditions. Originality/value: The findings indicate opportunities to improve embedding of school health promotion in the education sector and to invest in implementation support.