OBJECTIVES: Physical activity is associated with positive health effects and improved cognitive function in children. However, these data are primarily based on cross-sectional studies. We investigated changes in cognitive function, physical fitness and physical activity in children following a school-based intervention. METHODS: The 'fit4future' study is a prospective, interventional, long-term study conducted in Germany to evaluate the impact of a comprehensive school-based health promotion programme in children. The aims of the programme have been to increase the amount of physical activity, to support a healthy diet and to improve attention and concentration performance as well as coping strategies. Schools received equipment to support physical activity, for example, action cards, brochures as well as online materials containing information regarding physical activity, nutrition, cognitive function and stress management. Teachers were trained in six workshops to enable them to promote a systematic health promotion process at schools. Parents received brochures about healthy lifestyles with practical advice for everyday family life. Additional information was provided on the programme's homepage. At the beginning of the second and the end of the third grade, children completed a differential performance test (Concentrated Task) for the assessment of concentration and attention in which they had to cross predetermined pictorial symbols on preprinted test sheets (average marked signs). Changes in the average marked signs were investigated and compared with age-specific and sex-specific norms. Physical fitness and activity were assessed using a six-item fitness test and questionnaire. RESULTS: A total of 839 children (mean age 7.5±0.6 years, 48% girls) from 32 schools participated in this study. Over 2 years, average marked signs increased from 91.6±20.7 to 138.0±27.6 (p<
0.001) (n=553 children, mean age 7.5±0.6 years, 51% girls). This improvement was greater than expected compared with the age-specific and sex-specific norms. The children showed significant improvements in all fitness test items and a significant increase in physical activity (p<
0.001). Age, baseline average marked signs and changes in the jump-and-reach test were associated with changes in cognitive function (regression coefficient β=0.95, SE=0.23, p<
0.001). CONCLUSION: A school-based health promotion programme improved cognitive function, physical activity and physical fitness beyond the age-related improvements expected over 2 years in a large cohort of primary school children. TRIAL REGISTRATION NUMBER: German Clinical Trials Register (DRKS-ID: DRKS00020894, Date of registration: 2020-02-26).