As prevention programs become disseminated, the most serious threat to effectiveness is maintaining the quality of implementation intended by the developers. This paper proposes a methodology for measuring quality of implementation in school settings and presents data from a pilot study designed to test several of the proposed components. These methods included assessments of adherence, quality of process, the positive or negative valence of adaptations, teachers' attitudes and teachers' understanding of program content. This study was conducted with 11 teachers who had varying degrees of experience who taught Life Skills Training. Observation and interview data were collected during visits to schools. Results suggest that quality of implementation can be measured through observation and interview. Teachers varied in adherence and quality of program delivery. All teachers made adaptations to the program. Experienced teachers were more likely to adhere to the curriculum, deliver it in a way that was more interactive and engaging to students, communicate the goals and objectives better, and make positive adaptations. The field can use these findings as the basis for exploring strategies for measuring and improving quality of implementation.