Abstract A major issue in smoking prevention research is that no study has tried to equate program success expectancies across experimental and placebo control conditions. Equivalent overall program success expectancies should be established to help rule out the effects of extra-theoretical variables which influence program outcomes. The present study tested whether an attention-placebo (information based) smoking prevention program would produce equivalent expectancies about the likelihood of program success in comparison to an experimental social influences program. To try to equate program success expectancies, the design of the two programs differed in content but was similar in procedure. Fourteen middle schools were randomly assigned to the two conditions. As hypothesized, baseline expectancies were found to predict outcome measures, even after controlling for baseline smoking intentions, ethnic group, and gender. Second, the equivalence of program expectancies at posttest was tested. Youths held equivalent overall expectancies for success across conditions. This study suggested the need to control for program expectancies in prevention research, and showed that program expectancies could be controlled for by equating process of program delivery.