This cooperative agreement (RFA HL-00-011) application is for a field center for the collaborative, multi-center "Trial of Activity for Adolescent Girls" (TAAG) study. The primary aim of the six-year study is to prevent the decrease in physical activity (PA) and fitness in adolescent girls through a school-based, community-agency-linked intervention aimed at encouraging PA in school and after school during the 7th and 8th grades. Six vanguard middle schools with a large minority population and a diverse group of agencies (Tucson City Parks and Recreation, YMCA, Boys and Girls Club, PLAY, Amphitheater Extension program) have agreed to participate. Herein we outline strategies for designing a culturally sensitive intervention, based on formative assessment, and guided by the social-ecology framework of Well's "Youth Physical Activity Promotion Model." In-school PA will be increased through enhanced physical education, using the ACTIVITYGRAM and FITNESSGRAM, for motivation and evaluation. Issues of perceived self- worth, body-image, self-efficacy, overcoming PA barriers and other psychosocial mediators of PA will be addressed in health and PE lasses and after-school through an innovative Wellness Theater and Dance approach. Other appealing activities for adolescent girls will be offered after school through agency involvement, e.g., dance and creative movement, martial arts, individual and some team sports. Special events will promote family and community involvement. Physical activity will be assessed by the ACTIVITYGRAM and accelerometers, and fitness by the PWC 170 test. Innovative secondary aims focus on relationships and intervention effects on body image and self-esteem and programs, physical activity patterns, tobacco and drug use, sexual activity, weight concerns, school attendance and academic achievement., Formative assessment and pilot testing of intervention components and assessment instruments will be done during a two-year feasibility phase. Findings from focus groups, interviews and observations with adolescents, parents, and school and agency personnel will guide intervention design. Early and on-going community and agency involvement will foster partnerships and promote sustainability. Our multi-disciplinary team of exercise scientists, nutritionists, epidemiologists, and physical educators has over 15 years of experience in multi-center, collaborative trials (coordinating center and field center) in children and adults. The team brings expertise in PA program design, PA and fitness assessment, formative assessment, behavior theory and curriculum development, intervention delivery, process evaluation, and data management.