Canadian researchers tracked the school sport participation and mental health of 853 students from grades 8-12. They found that after 5 years, those who were involved in teams sports at school had less depressive symptoms, lower perceived stress and a more positive self-image. Specific causes aren't clear, but researchers hypothesize it may be related to the social bonds fostered in playing together.
PositiveTip: Encourage your teen to join a school team sport they enjoy.