Institutional Review Board Statement
Approval for the study was obtained from the ethics committee of the Center for Psychosocial Medicine at the University Medical Center Hamburg Eppendorf and the responsible school authorities at each study site (Center for Education Monitoring and Quality Development at schools in Hamburg, IfBQ; the Center for Prevention at the Institute for Quality Development at Schools in Schleswig-Holstein, IQ.SH; and the Bavarian State Ministry for Education and Cultural Affairs) prior to data collection. The study is conducted in accordance with the CONSORT guidelines and complies with the principles laid down in the Declaration of Helsinki. It is registered in the DRKS public database (trial registration number DRKS00023788). Written informed consent was obtained from all participants prior to study enrollment. All substantial protocol deviations or modifications were communicated to the Ethics Committee and DRKS register.