A three-wave study over one year with 882 adolescents, aged 10 to 16 years at the initial testing, examined psychosocial variables regarding four health-related behaviors: exercise, eating fruit, smoking, and drug use. Analysis showed that during the stages of the study, high school students' exercise behavior decreased and their smoking behavior increased as well as their willingness to use drugs. It seems that study of physical education and health education during adolescence must take into account the possible differences in psychosocial variables associated with health-related behaviors as well as the different stages of adolescence.