The objective of this study was to assess changes in adolescent girls' health-enhancing cognitions and behaviors targeted by the Go Girls! group-based mentorship lifestyle program. Three hundred and ten adolescent girls (nested within 40 Go Girls! groups) completed questionnaires that assessed cognitions (attitudes, self-regulatory efficacy, and intentions) and behaviors (physical activity and dietary) at four time points (two pre-program, one at the end of the program, and one at 7-week follow-up [5]. In response to these public health concerns, genderspecific lifestyle interventions have been developed for adolescent girls that target health behaviors, such as physical activity and dietary behaviors, and cognitions toward those behaviors.The majority of gender-specific lifestyle interventions for youth have tended to focus on the prevention or treatment of obesity [e.g., 6, 7]. For example, Neumark-Sztainer and colleagues [8] examined the effectiveness of a physical education program entitled "New Moves" to target health behaviors and body image among adolescent girls at risk of overweight and obesity. Results from this study [8] indicate that after completing the program, girls reported significant improvements in portion control, reductions in sedentary behavior, and increases in their physical activity self-efficacy and self-reported psychological "stage of change" for both dietary and physical activity behaviors. However, no significant changes were found for physical activity behavior or quality of dietary intake in terms of consumption of fruit and vegetables and sugar-sweetened beverages. Similarly, findings from another school-based lifestyle program for adolescent girls indicated improvements in girls' health behavior intentions and dietary knowledge, but no changes in physical activity or dietary behavior after completing the program [9].In light of the limited effectiveness of these programs, theory-based research is needed to target behavior change. Specifically, the social context has