ABSTRACT
Abstract This study examines the influence of social support on bystander behaviors, the mediating and moderating effects of moral disengagement and defender self-efficacy at the individual and class levels, and their cross-level interaction. A total of 1310 children in grades 4-6 completed our questionnaire survey at four-time points between October and December in 2021. The questionnaires include the Scale of Perceived Social Support (T1), Moral Disengagement Scale (T2), Defender Self-Efficacy Scale (T3), and Bullying Participant Behaviors Questionnaire (T4). The multilevel moderated mediating model results show that (1) social support negatively predicts reinforcer and outsider behavior and positively predicts defender behavior; (2) defender self-efficacy plays a mediating role between social support and defender behavior, moral disengagement plays a mediating role between social support and bystander behaviors, and defender self-efficacy and moral disengagement play a chain mediation role between social support and bystander behavior; (3a) class-level defender self-efficacy has a direct impact on defender behavior and moderates the relationship between individual defender self-efficacy and reinforcer behavior; and (3b) class-level moral disengagement has a direct impact on defender and outsider behavior and a cross-level moderated role between individual moral disengagement and reinforcer behavior. These results show that the individual and class level defender self-efficacy and moral disengagement can influence the bystander behavior of primary school students, which is of great significance for schools to develop anti-bullying moral education courses and design measures to improve students' anti-bullying self-efficacy.