Objectives Our large-scale cluster randomised controlled trial aimed to investigate the effects on health knowledge and enjoyment of an 11 week ‘health education through football’ programme for children aged 10–12 years old. Methods 3127 Danish school children (49% girls) aged 10–12 years from a total of 154 schools located in 63% of the Danish municipalities (69 of 98) took part in the analysis. A 5:1 cluster randomisation was performed at school level for the intervention group (IG) or the control group (CG). The twice-weekly 45 min intervention was the ‘11 for Health in Denmark’ programme, which includes health education, football drills and small-sided games. The health education element focused on hygiene, nutrition, physical activity and well-being. Outcomes: The participants completed a 34-item multiple-choice computer-based health knowledge questionnaire preintervention and postintervention. IG also evaluated whether the programme was enjoyable. Results Between-group differences (p<0.05) were observed in overall health knowledge in favour of IG (+7.2% points, 95% CI 6.1% to 8.4%, effect size, ES:0.59), with similar effects for girls (+7.4% points, 95% CI 5.9% to 9.0%, ES:0.57) and for boys (+7.0% points, 95% CI 5.3% to 8.7%, p<0.05, ES:0.51). Marked between-group differences were observed in favour of IG, for health knowledge related to hygiene (IG vs CG:+13.9% points, 95% CI 11.1% to 16.7%, ES:0.53), nutrition (+10.3% points, 95% CI 8.5% to 12.1%, ES:0.53), physical activity (+5.9% points, 95% CI 4.1% to 7.7%, ES:0.36) and well-being (+4.4% points, 95% CI 2.7% to 6.1%, ES:0.28). Both girls and boys gave the programme moderate to high scores for enjoyment (3.6±1.0 and 3.7±1.1, respectively). Conclusion Health education through sport, using the ‘11 for Health’ model, was enjoyable for girls and boys aged 10–12 years old, and improved health knowledge related to hygiene, nutrition, physical activity and well-being.