Drawing on the elaboration likelihood model of persuasive communication, the authors examine the impact of the perceptions of the instructor or source on students' receptivity to a new substance abuse prevention curriculum. Using survey data from a cohort of students participating in the Adolescent Substance Abuse Prevention Study, the authors use structural equation modeling to determine the effects of the perceptions students have of their program instructor on measures of the targeted program mediators and the use of cigarettes, alcohol, and marijuana. They test these instructor effects after each component of a two-part curriculum is administered (during the seventh and ninth grades). They find that the perceptions of the instructor significantly affect refusal, communication and decision-making skills, normative beliefs, perceived consequences of use, and substance use. The authors discuss the implications of these findings for school-based prevention programming and indications for further research. (Contains 10 notes and 3 tables.)