back The effects of a social network method for group assignment strategies on peer led tobacco prevention programs in schools T W Valente Objective. To test the effectiveness of a network method for identifying peer opinion leaders and constructing groups. Methods. Three conditions (random, teacher, and network) were randomly assigned to 84 6th grade classrooms within 16 schools. Pre- and post-curriculum data were collected from 1,961 students on mediators to tobacco use. The network condition consisted of identifying peer leaders using student nominations and matching those leaders to students who nominated them. Results. Students in the network condition liked the prevention program more and had improved attitudes (â=-0.06; p<.01), improved self-efficacy (â=-0.10; p<.001), and decreased intention to smoke (adjusted odds ratio = 0.46, 95% CI = 0.38, 0.55). Conclusions. The network method was the most effective means for structuring the tobacco prevention curriculum and can be improved and further tested in multiple settings to improve health promotion efforts.