Abstract
This three-armed randomized controlled trial examined how moral disengagement and social norms account for change in bullying behavior and their potential as targets of anti-bullying components within separate interventions among 1200 French-speaking Belgian elementary students (48% boys, 9–12 year-olds, 57 classes, nine schools) during 2018–2019 (no ethnicity data available). Mediation analysis revealed that students’ moral disengagement successfully decreased (β = −.46), which, in turn, reduced both bullying (β = .33) and outsider behaviors (β = .20), and increased defending (β = −.10). Intervening on social norms decreased bullying (β = −.18), but not through the perceived injunctive class norm as intended. Guidelines to open the “black box” of anti-bullying programs and determine the cost-effectiveness ratio of their components are provided.