This study measures the nationwide participation rates of girls and boys in exercise and organized team sports. The central focus is on how the intersections among families, schools and communities are related to children's involvement and interest in athletics and physical activity. Some of the personal and social benefits associated with children's athletic participation are also identified and discussed. The athletic interests and involvements of girls and boys are examined from childhood through late adolescence, including entry into sport as well as drop-out patterns. Appended are: (1) National Policy Advisory Board; and (2) Research Design and Methods. (Contains 173 tables, 6 figures and 50 endnotes.)