Esther Mertens

| 51 Effectiveness of a Psychophysical Intervention weekly during 90-minute physical education lessons. Trainers were teachers of the schools, mostly physical education teachers as they have experience with teaching physical activities in class. During the lessons, students participate in physical exercises and games, reflect on the exercises, share and discuss their thoughts with each other, and address how to use the learned skills in their daily lives (see the study protocol for more information Mertens et al., 2018). Condition check. In the ‘Light’ condition a core team of teachers followed the 3-day training to become certified R&W trainers and implemented the intervention. In the ‘Standard’ condition a core team of teachers was trained to implement R&W (i.e., R&W trainers) and the rest of the teaching staff received a 3-day training to learn how to support the R&W trainers and how to apply R&W in their regular classes. The ‘Plus’ condition was equal to the ‘Standard’ condition with the addition of a parent component; parents were invited to watch a documentary about R&W, join a R&W lesson in the school, received weekly e-mails with information about the R&W lesson of that week and were encouraged to act on this information. In all three conditions, the R&W trainers received supervision from their R&W coach during the implementation of the intervention. To examine whether the condition manipulation was successful, trainers and parents completed questionnaires after the first and second year of the intervention. As planned, more teachers in the Standard and Plus conditions than in the Light condition were involved in the intervention; in the Light condition only the R&W trainers (i.e., trained teachers) implemented R&W, whereas in the Standard and Plus conditions it was reported that the R&W trainers as well as other teachers applied the intervention techniques. Furthermore, in the Plus condition parents were involved in the intervention; parents reported that they read the weekly information sometimes (57%) or often (39%), and some parents indicated they watched the documentary of R&W (15%) and participated in a R&W lesson at their child’s school (23%). In addition, parents in the Plus condition reported to have implemented parts of the intervention more often at home than parents in the Light and Standard conditions. In conclusion, the involvement of teachers and parents was in accordance with the study design of the conditions. Intervention fidelity. Intervention fidelity was assessed with two complementary methods: Self-reports of R&W trainers and observations of 67 R&W lessons by 3 R&W experts. R&W trainers completed a questionnaire about fidelity after each third lesson in the first year of the intervention and after each second lesson in the second year. R&W experts completed a coding schema based on Bishop and colleagues (2014) during the observation. According to the self-reports, R&W trainers were generally able to mostly complete lessons (65%) and did not deviate or only slightly deviated from the manual (72%). R&W experts indicated that most observed lessons were completed or almost completed (86%). Trainers did not deviate much from the manual (91%). When trainers did adjust the intervention, these adjustments were generally judged as improvements (62%). 3