Bullying is a peer relational problem that can inflict psychological harm onto both those who are victimized and those who witness it occur. Fostering a positive classroom environment is an important protective factor in preventing bullying. Authoritative classroom climates may protect victimized and bystander youth from negative mental health outcomes associated with bullying involvement. The current study examined how dimensions of authoritative classrooms -- disciplinary structure and teacher support -- moderate the relationship between bullying involvement (e.g., victimization, witnessing) and students' psychological functioning (e.g., psychosocial wellbeing, emotional problems). We explored how authoritative classroom climate may protect victimized and bystander youth across different cultural contexts. Multilevel regression analyses were conducted on two separate samples of youth, from China (2,395 students in grades 5-9, from 58 classrooms across 5 schools), and Canada (538 students in grades 5-8, from 31 classrooms across 5 schools). Findings indicated that both victimization and witnessing were associated with lower psychosocial wellbeing and higher levels of emotional problems among Chinese and Canadian youth. For Chinese youth, witnessing was less strongly associated with lower psychosocial wellbeing in classrooms with higher disciplinary structure. In contrast, witnessing was more strongly related to emotional problems and lower psychosocial wellbeing in Chinese classrooms with higher teacher support. Collectively, these findings suggest that bullying negatively affects the mental health of the broader school community across both Chinese and Canadian contexts. In more collectivist cultures, promoting classroom climates that regulate student's behaviors by enforcing discipline fairly and consistently may help lower distress among students who witness bullying.