Physical Activity and Body Composition Outcomes of the “Primary School as a Whole-Day School” Program in Early School-Age Children from Croatia

Physical activity (PA) and body composition (BC) are important indicators of overall health, especially in children, with the school environment being a key setting for the promotion of PA and prevention of overweight and obesity. This study aimed to evaluate the effects of a specific national experimental schooling program (“Primary School as Whole-Day School”) on changes in PA and BC in early-school-aged children in Croatia. The participants were 128 children aged 9–11 years from southern Croatia (53 girls) who participated in whole-day (n = 54, 20 girls) or regular-schooling-programs (n = 74, 33 girls) over a period of one school year (9 months). A pre-to post-measurement design was applied, with directly (via GENEActiv accelerometers) and indirectly (by PAQ-C questionnaire) measured PA, and body composition measurements (via bioimpedance analysis) as independent variables. A multifactorial ANOVA (Group × Gender × Time) was applied to evaluate the effects. The results indicated significant (p < 0.05) ANOVA effects for indirectly measured PA and the accelerometer-derived moderate-to-vigorous PA, with favorable changes in the whole-day schooling group. The changes in directly measured PA were particularly evident in boys involved in whole-day schooling. There were no significant effects of the experimental program on body composition. While the experimental program was effective in increasing PA, the lack of positive changes in body composition could be explained by the relatively short study period and the absence of accompanying dietary strategies. Although promising, the results highlight the complexity of influencing health-related outcomes in early-school-aged children.