Although comprehensive school-wide interventions targeting bullying have proven effective, many schools, particularly those in low-to-middle income countries like Pakistan, lack the necessary resources to implement them. As a result, implementing cost-effective antibullying bystander programs that train students to become peer advocates is a promising approach for intervening in bullying incidents. Peer training in antibullying intervention involves training students to take on leadership roles and advocate for antibullying initiatives within their school communities. The aim of this study was to design, implement, and evaluate a peer-training module that was subsequently implemented in four schools (N = 38, boys = 26, girls = 12) in Pakistan. The aim was to raise awareness and prepare a team of peer mentors to effectively implement antibullying policies in educational institutions. Pre-post tests and participant feedback were used to evaluate the effectiveness of the peer-training program in increasing knowledge and awareness of bullying and the role of bystanders among trained peer mentors. To determine the impact of the peer mentor training on improving the school environment, data were also collected from students (N = 219, boys = 152, girls = 67) before and after the implementation of the program. The pilot implementation of the peer-training module was considered successful, indicating that the training was effective in improving the knowledge of peer mentors and could be used in a similar way in future cases. The results also showed a significant improvement in the development of prosocial bystanders. However, although improvements were observed in other aspects of the school environment, these did not reach statistical significance. The discussion section includes recommendations and explanations for differences based on gender and urban–rural factors. Suggestions are also made to improve the results for future applications.