Cluster randomized control trial to reduce peer victimization: An autonomy-supportive teaching intervention changes the classroom ethos to support defending bystanders.

Peer victimization is a worldwide crisis unresolved by 50 years of research and intervention. We capitalized on recent methodological advances and integrated self-determination theory with a social-ecological perspective. We provided teachers with a professional development experience to establish a highly supportive classroom climate that enabled the emergence of pro-victim student bystanders during bullying episodes. In our longitudinal cluster randomized control trial, we randomly assigned 24 teachers (15 men, 9 women; 19 middle school, 5 high school; 32.8 years old, 6.7 years of experience) in 48 classrooms to the autonomy-supportive teaching (AST) workshop (24 classrooms) or the no-intervention control (24 classrooms). Their 1,178 students (age: M = 13.7, SD = 1.5; range = 11-18) reported their perceived teacher autonomy support; perceived classmates' autonomy support; adoption of the defender role; and peer victimization at the beginning, middle, and end of an 18-week semester. A doubly latent multilevel structural equation model with follow-up mediation tests showed that experimental-group teachers created a substantially more supportive classroom climate, leading student bystanders to embrace the defender role. This classroom-wide (L2) emergence of pro-victim peer bystanders led to sharply reduced victimization ( effect size = -.40). Unlike largely unsuccessful past interventions that focused mainly on individual students, our randomized control trial intervention substantially reduced bullying and victimization. Focusing on individual students is likely to be ineffective (even counterproductive) without first changing the normative climate that reinforces bullying. Accordingly, our intervention focused on the classroom teacher. In the classrooms of these teachers, bystanders supported the victims because the classroom climate supported the bystanders. (PsycInfo Database Record (c) 2023 APA, all rights reserved).