This study examined the effectiveness of a tobacco and alcohol prevention program that was delivered to sixth and seventh grade students by minimally trained classroom teachers. The program focused on (a) teaching students to identify and resist peer influences, (b) information about short- and long-term consequences of tobacco and alcohol use, (c) the correction of normative expectations, and (d) the establishment of conservative intentions regarding tobacco and alcohol use. Two cohorts of students were pretested, and subsequent to delivery of the program, they were tracked longitudinally. The first cohort was followed for four years, the second was followed for three years. Results indicate that the program reduced the onset and prevalence of tobacco use but not alcohol use. The effects for tobacco were differentially related to the school district in which the program was delivered, the sex of student, and ethnicity, suggesting that prevention program content is only one variable that may affect the effectiveness of prevention interventions.