Study design
The ACTIVE CLASS study is a RCT, with randomization at school level [ACTIVE CLASS is a multicenter study whose management is designed to ensure effective collaboration and communication between research groups. The research groups consist of qualified researchers and graduates in PA and sport sciences from two Universities (University of Cadiz and University of Extremadura, Spain). Both Research groups adhere to a common study protocol for training, fieldwork, data collection and management, and quality control procedures. There is continuous telematic contact during the development of the study. In addition, each research group has responsible investigators who manage the day-to-day running of the study in their centers and are in continuous contact with their counterparts at the other university to make decisions on aspects that require a quick response or do not require a meeting of all the in researchers.