BackgroundWhile positive school climate is important for students’ well-being and mental health, school personnel may experience challenges in creating a nurturing school climate. School-Wide Positive Behavioral Interventions and Supports (SW-PBIS) has shown positive effects on school climate and children’s prosocial behaviors, but fewer studies have been conducted in a European context.AimThis project aims to investigate the effectiveness of SW-PBIS program for students’ social-emotional skills and academic achievement as well as teachers’ and students’ perceptions of classroom learning environment. Furthermore, the study intends to evaluate how school-level factors mediate or moderate the effects of the intervention. In addition, the study includes a qualitative evaluation of the dynamic interaction processes that occur during program implementation in local school contexts.MethodsData on school- and individual-level measures are collected in intervention and control schools. With regard to challenges in retaining control groups over extended time periods, two waves of recruitment are used. In the first wave, an active control group is used and data are collected during three time points. In the second wave, a wait-list control group will be used and data will be collected during two time points during one school year. Hierarchical regression analyses will be conducted to explore the effects of SW-PBIS on the outcomes of the study. An ethno-methodological approach will be applied to provide a detailed examination of the social interactional and meaning-making practices of different school implementation teams, and the negotiation of normative expectations and rules of conduct in peer-teacher-student interactions in different classrooms.DiscussionThe study is expected to contribute to knowledge on the effects of the SW-PBIS program and how these effects may be mediated or moderated by school-level factors. Combining quantitative and qualitative methods to explore the significance of school contexts in the implementation of the SW-PBIS program constitutes the strength of the study. The challenge in the study is the extended period of implementation of SW-PBIS, which entails difficulties in retaining a control group over the required time period. Therefore, two waves of recruitment are used, encompassing different procedures of allocation to intervention or control group.Trial registrationClinicalTrials.gov Identifier: NCT06270914 on the 22nd of February, 2024 (retrospectively registered).