The present study examined contextual and individual predictors of attendance in a 10-session school-based teen smoking cessation program. Participants were 349 students at 29 Illinois high schools. Predictor variables included demographics, smoking history, psychosocial variables, and social environment variables. School-level characteristics of interest included proportion of low-income students, group size, and program timing. Overall attendance was predicted by higher motivation and less stress at baseline. Students also were more likely to attend if they had already tried to quit, were more dependent on nicotine, and had more positive smoking expectancies. Percentage of low-income students and program timing also predicted program attendance; students were more likely to attend the program at schools with lower percentages of low-income students and where the program was offered during the school day. We also examined predictors of attendance before and after quit week (week 5). Early in the program, only the school-level variables (program timing and percentage of low-income students) predicted attendance. After quit week, the school variables also were important, and baseline motivation and perceived stress also predicted attendance at these sessions. Results highlight the importance of individual characteristics in determining program participation, as well as the importance of considering school context and programmatic issues when planning school-based smoking cessation programs.