The project will develop an intervention to promote healthy sleep behaviour in adolescents. The intervention will be based on a participatory health research approach to promote healthy sleep behaviour in adolescents. Because healthy sleep behaviour is associated with a healthy lifestyle overall, the intervention will additionally focus on healthy eating patterns, sedentary behaviour and physical activity. In order to become the most effective intervention, adolescents will participate during every step of the intervention development.

Three school in Flanders are contributing to this project on a voluntary basis. All adolescents age 13 to 15 of the intervention schools were invited to participate in the study by an informative session at the school, where they were informed about the importance of their involvement in the study and the aim of the intervention. The adolescents who gave their consent, were invited to participate in a workshop were skills needed for participatory research were trained. Afterwards, an action group (6 - 8 pupils) was conducted at each school. Brainstorm sessions about effective strategies to change sleeping behavior in this population. Strategies, perceived as effective by the target population, will be summarized in an overview. Also feedback of adolescent, who are not part of the action group, will be asked. After feedback, the intervention will be developed by the intervention schools. Thereby, three different intervention strategies will be implemented and tested (one intervention at each school) to meet the individuals needs of each school. Right now, the action groups are busy conducting the intervention materials during a weekly 1-hour session. This session is accompanied by two researchers to provoke brainstorm sessions and creativity. The researchers facilitate the process, stimulates creativity, organize and keep track of the feasibility of ideas. After the development of intervention materials, the intervention will be implemented in the school by the adolescents themselves, in collaboration with teachers and the two researchers.

Overall, can be stated that a group oriented approach will be used during the whole intervention. For example, plenary speakers will give information about sleep hygiene, physical activity breaks will be introduced, sleep behaviour will be discussed in class, active transport will be stimulated, a campaign on social media will be started, and informative flyers/posters about sleep, screen time, physical activity and nutrition will be spread in the close neighborhood, a competition between class groups will be started (based on objective data collected using activity trackers).

The intervention will be analysed using a clustered randomized controlled trial, including three intervention schools and six control schools. These schools were recruited in Flanders, the Northern part of Belgium, via convenience sampling. The head of each school was contacted via telephone. When the head of the school gave consent, all adolescents age 13 - 15 and their parents were invited to participate in this study. All adolescents who gave their consent, were pre-tested (between November 2017 and January 2018). The pre-test included a questionnaire investigating determinants of sleep and a wearable activity tracker to objectively measure the sleep duration. The questionnaires were developed based on the 'Munich ChronoType Questionnaire', 'The School Sleep Habits Survey', 'Sleep Knowledge Questionnaire', 'Sleep Hygiene Index' and 'Paediatric Daytime Sleepiness Scale'. Focus groups were organized to determine relevant determinants. The understandability of the questionnaire was tested with the 'Thinking aloud protocol' and validation testing was performed. After implementing the intervention at the intervention schools, an effect-evaluation will be conducted based on a pre-,post and follow-up testing and a process evaluation will be performed.