The data was collected for the TRIAL: TRansitions Into Active Living study funded by NWO (grant no.: NWA.1160.18.249). The original aim of the this study was to examine changes in physical activity and sports during the life transition ‘from primary to secondary education’. Secondary school students were enrolled in the study in October 2020, shortly after they transitioned from primary to secondary education, and were followed until November 2022, shortly after they transitioned to their third year of secondary education. Seven waves of data collection took place. We collected data using questionnaires, motor skill test items, and height and weight measurements.