The phenomenon of bullying/victimization affects millions of students globally and is associated with enduring consequences and internalizing problems for all the participants. Drawing upon Bandura's Social Cognitive Theory, this study examines the moderating effects of individual attributes (gender and educational stage) and environmental factors (social support size and social support satisfaction) on the relationship between self-efficacy and bullying/victimization involvement, to address a pervasive issue in schools. The sample consists of 1,178 Greek students, from the fifth and sixth grades of primary school and the seventh, eighth, and ninth grades of secondary school. Students completed measures of bullying/victimization, self-efficacy, and social support. Present findings suggest that both individual attributes and environmental factors may influence the relationship between self-efficacy and bullying involvement. Moreover, social support was found to have differential moderating effects for bullying and victimization, highlighting the importance of quality relationships in school. The implications of these findings are significant for educators, policymakers, and researchers alike. Understanding the moderating effects of gender, educational stage, and social support on the relationship between self-efficacy and bullying/victimization involvement can inform the design of targeted interventions.