Background: The present study investigates the well‐being effects for 10‐ to 12‐year‐old children  who participated in the school‐based intervention “11 for Health in Denmark,” which comprises physical activity (PA) and health education. Subgroup analyses were carried out for boys and girls.

Method: Three thousand sixty‐one children were randomly assigned to an intervention group (IG) or a control group (CG) by 5:1 cluster randomization by school. 2533 children (mean age 11.5 ± 0.4; 49.7% boys) were assigned to IG and 528 children (mean age 11.4 ± 0.5; 50.8% boys) were assigned to CG. IG participated in the “11 for Health in Denmark” 11‐week program, consisting of 2 × 45 min per week of football drills, small‐sided games, and health education. CG did not participate in any intervention and continued with their regular education. Before and after the intervention period, both groups answered a shortened version of the multidimensional well‐being questionnaire KIDSCREEN‐27.

Results: The “11 for Health in Denmark” intervention program had a positive effect on physical well‐being in girls (IG: 48.6 ± 8.5 to 50.2 ± 9.3), whereas the improvement was not significant in boys. The program also had a positive impact on well‐being scores for peers and social support (IG: 50.2 ± 10.2 to 50.8 ± 10.1), though when analyzed separately in the subgroups of boys and girls the changes were not significant. No between‐group differences were found for psychological well‐being or school environment.

Conclusion: The intervention program had a positive between‐group effect on physical well‐being in girls, whereas the change was not significant in boys. The overall scores for peers and social support improved during the intervention period, but no subgroup differences were found.

 © 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.