While researchers have developed more effective programs and strategies to prevent the initiation of substance use and increasingly communities are delivering these interventions, determining the degree to which they are delivered as they were designed remains a significant research challenge. In the past several years, more attention has been given to implementation issues during the various stages of program development and diffusion. This paper presents the findings from a substudy of an evaluation of a newly designed middle and high school substance abuse prevention program, Take Charge of Your Life delivered by local Drug Abuse Resistance Education officer instructors. A key aspect of the study was to determine the extent to which implementation fidelity, using the measures of content coverage and appropriate instructional strategy, was associated with improvement in the program mediators of realistic normative beliefs, understanding the harmful effects of substance use and the acquisition of decision-making and resistance skills. Although it was found that higher fidelity was associated with better scores on some of the mediators, this was not a consistent finding. The mixed results are discussed within the context of the lesson activities themselves.