The CTT program is based on a network of community-based organizations that coordinates substance abuse prevention activities, conducts strategic planning and data collection, and provides staff development training. The study identified aspects of the CTT program that were related to outcome changes in order to better understand what accounted for the culturally responsive nature of the program. CTT participants were more knowledgeable about drugs and about negative influences of drugs after completing the program during the school year. In addition, there was a significant increase in school-based social comfort following participation in the program. For parents, there was a significant increase in school competence but no significant change in their perceptions of family relations. The CTT program produced much less effect on youth and family participants when it was conducted in the summer in that no pre-post outcome changes were found for the summer-based intervention. Outcome differences between school and summer programs were associated with specific types of curriculum-based dosage differences. Ways in which dosage differences between school and summer programs may have contributed to observed outcome differences are discussed. 14 references and 5 tables