Data collection
Simple random assignment was used to assign the schools into the experimental and the control groups, with one school in each group. The students in grade seven and eight, at both schools, also were randomly selected from one classroom in each grade. The selected students were Thai adolescent girls who were willing to be participants in this study. Baseline data were collected from both the experimental and control groups using the questionnaires. After that, all study participants were tested to determine their physical fitness. During the first session, both groups received general information on physical activity and a physical activity booklet for adolescents. The experimental group also received the physical activity promotion program of three sessions per