Our project integrates a multidimensional intervention to promote physical activity, with a mixed design (cross-over randomized trial, and a qualitative study) and consist of two sub-projects that share the same study population: "Effectiveness of an intervention of physical activity promotion in schoolchildren on preventing obesity during the adiposity rebound period: a cross-over randomized cluster trial" and "Effectiveness of physical activity intervention to prevent obesity and improve academic performance in children with and without ADHD risk".