Background: Bullying behavior in schools can lead to psychosocial problems. School-based interventions are important in raising student awareness, developing their skills and in planning to reduce bullying behavior. Methods: A randomized controlled trial, using a school-based educational intervention to reduce verbal bullying, was conducted among grade 10 students in 16 urban and rural schools in KwaZulu-Natal, South Africa in 2013. Baseline and postintervention questionnaires, developed using the Integrated Model for Behavior Change theoretical model, were used to assess changes in verbal bullying. Results: Postintervention there were reduced verbal bullying experiences. Improved social norms and awareness of verbal bullying were associated with reduced verbal bullying experiences and behavior. Although less likely to bully others verbally, girls were more likely to experience verbal bullying. Students with no living father were more likely to bully others verbally. Conclusions: The study findings indicate that a school-based intervention can positively impact on verbal bullying experiences and behavior.