Project S.H.O.U.T. (which stands for "Students Helping Others Understand Tobacco") is a tobacco-use prevention project funded by the United States National Cancer Institute for preventing the use of cigarettes and smokeless tobacco (snuff and chewing tobacco) in public schools in San Diego County, California. Based on principles of behavior modification, Project S.H.O.U.T. teaches students how to anticipate and overcome negative peer pressure to use tobacco and reinforces them for having done so. Preliminary results indicate that the prevalence of tobacco use among students receiving peer pressure resistance skills training was somewhat but not statistically significantly lower than the control group after one year of intervention. In addition, students in a third lottery condition, who were reinforced for simply not using tobacco, showed lower prevalence rates compared to controls. Additional support for the efficacy of the intervention program was provided by the refusal skills assessment test, which indicated that students exposed to the intervention were able to refuse tobacco offers more effectively than the control students. Our results indicate that tobacco use prevention experts should do more than provide decision-making and behavioral skills for resisting tobacco use, but should also reinforce the non-use of tobacco.