This dissertation aimed at examining the adaptation, implementation, and evaluation of a comprehensive school reform in French-speaking Belgium, that is School-Wide Positive Behavior Interventions and Supports (SWPBIS). The general introduction points out the importance of school climate and the role of teachers’ collective efficacy based on results from international surveys and on the literature. The research context and SWPBIS are presented, before introducing the research project, its objectives, and the hypotheses. The introduction closes on an overview of the dissertation. The five articles introduce the results of the five conducted studies. The first one is a systematical and critical review of the existing literature concerning SWPBIS, its implementation and numerous outcomes. The second article is a comparison of SWPBIS implementation in three French-speaking contexts. This exploratory study’s goals were to highlight the similarities and differences between the implementation in the three contexts and to analyze the unmissable facilitating factors that anyone interested in implementing SWPBIS should be aware of. The third article is the result of cross-cultural study on school climate and mental health in teenagers. The study aimed at cross-culturally validating a school-climate survey and investigating the relation between school climate and mental health for secondary school students. The fourth article presents the results of the cultural adaptation of SWPBIS to the school context of French-speaking Belgium and the outcomes of SWPBIS implementation on school climate for all stakeholders: staff members, students, and parents. Results concerning the impact of SWPBIS implementation on tardiness and absenteeism are also presented. The fifth article examines the outcomes of SWPBIS implementation on teachers’ collective efficacy. The five articles are followed by a general discussion in which the initial hypotheses are confronted to the results of the five conducted studies. Then, the discussion takes ...