Objectives. We assessed a school-based intervention designed to promote tobacco control among teachers in the Indian state of Bihar. Methods. We used a cluster-randomized design to test the intervention, which comprised educational efforts, tobacco control policies, and cessation support and was tailored to the local social context. In 2009 to 2011, we randomly selected 72 schools from participating school districts and randomly assigned them in blocks (rural or urban) to intervention or delayed-intervention control conditions. Results. Immediately after the intervention, the 30-day quit rate was 50% in the intervention and 15% in the control group (P = .001). At the 9-month postintervention survey, the adjusted 6-month quit rate was 19% in the intervention and 7% in the control group (P = .06). Among teachers employed for the entire academic year of the intervention, the adjusted 6-month abstinence rates were 20% and 5%, respectively, for the intervention and control groups (P = .04). Conclusions. These findings demonstrate the potent impact of an intervention that took advantage of social resources among teachers, who can serve as role models for tobacco control in their communities.