Two studies investigated the utility of a Cognitive-Behavior Change model in predicting adolescents' health behavior changes. The intervention specifically aimed at increasing students' knowledge of heart healthy habits, strengthening their beliefs, attitudes, and confidence regarding their ability to improve their health habits, and providing students with the skills to make the heart healthy decisions and behavior changes. Six hundred and sixty tenth-grade students in six high schools in communities covered by the Stanford Heart Disease Prevention Program's (SHDPP) Five City Project participated in the study. The socioeconomic status of the students in both studies ranged from low to upper middle class. Students were assigned to a treatment condition with the 5-6 session SHDPP intervention or a control (delayed treatment) condition. In both studies, students receiving the SHDPP intervention exhibited greater health improvements than did students in the control condition, as measured by pre-post self-report survey and behavioral observations. The most powerful predictors in changing adolescents' health behaviors were Behavioral Intentions, Knowledge, and Confidence components of the Cognitive-Behavior Change model. (Author/JD)