School-based health interventions often have limited and inconsistent effects. Although interpersonal communication likely is important, hardly any studies have investigated interpersonal communication of students with their friends, classmates, and parents about the health programs and health behaviors in school-based health interventions. In a two-wave prospective study of 389 adolescents focusing on three health behaviors (i.e., alcohol use, snack intake, and exercise), we addressed two aims. Our first aim was to investigate how student evaluations of a school-based health intervention influenced interpersonal communication about health behaviors (i.e., valence and frequency of conversations). Findings showed that positively evaluating a school-based health intervention increased how often students talked about the intervention with friends, classmates, and parents, as well as how they discussed the three health behaviors. Our second aim was to investigate the influence of interpersonal communication with friends, classmates, and parents on predictors of health behaviors. We found for conversational frequency that frequently discussing health behaviors resulted in healthier (more positive) predictors of exercise, but also in unhealthier (more positive) predictors of snacking and drinking. Furthermore, findings showed that positively discussing exercising, and negatively discussing snacking and drinking, resulted in healthier predictors of these behaviors. Our findings show that it is important to understand the impact of post-intervention communication and that post-intervention communication with peers and parents about health behaviors are predictors of health behavior.