The Moderating Role of the School Context on the Effects of the Healthy Primary School of the Future.

: The current study investigated the moderating role of the school context on the effects of a Dutch health promoting school initiative on children's health and health behaviors. : The study used a mixed-methods design. The school context ( = 4) was assessed by the characteristics of the school population, teacher's health-promoting (HP) practices, implementers' perceived barriers, school's HP elements, and dominating organizational issues. Outcomes included objectively assessed BMI z-scores and physical activity (PA), and parent and child-reported dietary intake. Analyses included linear mixed models (four intervention schools versus four control schools), and qualitative comparisons between intervention schools with similar HP changes. : Effects on outcomes varied considerably across schools (e.g., range in effect size on light PA of 0.01-0.26). Potentially moderating contextual aspects were the child's socioeconomic background and baseline health behaviors; practices and perceived barriers of employees; and organizational issues at a school level. : Similar HP changes lead to different outcomes across schools due to differences in the school context. The adoption of a complex adaptive systems perspective contributes to a better understanding of the variation in effects and it can provide insight on which contextual aspects to focus on or intervene in to optimize the effects of HP initiatives.