Preadolescence is the the most active age group, from a physical point of view, the fittest and healthiest. This reality hides, unfortunately, another one, less encouraging -from the beginning of adolescence, many youths considerably diminish their physical activity, or worse, they completely abandon it. The objectives of this research were to: identify the influence of leisure time activities on the behavior of middle school pupils, identify the way in which middle school pupils spend their leisure time, identify the ways to optimize the extracurricular activities. This research used: the bibliographical method, the pedagogical observation method, the statistical-mathematical method, the graphical representation method, the inquiry method, the observational experiment method. There are significant differences between the two applications of the questionnaire, regarding exercising during leisure time, to the way in which this is organized, and to the aggressive behavior. The results suggest that the young people are confronted with numerous conflicts that, most of the time, they try to solve in the manner of winner-loser, or loser-loser, this attracting a series of negative effects, such as: the diminishing of self-confidence, taking extreme sides and forming coalitions, moral dilemmas, difficulties in making decisions.