 Physical activity now is happening at school, and that's about it. About half of the young teens' daily physical activity occurs at school, but it accounts for just a fraction of their time there. So we knew that schools were a major source of physical activity for kids, but we were surprised that kids spent only 4.8% of their time at school physically active. The lowest of all locations, said study lead author Jordan Carlson, director of community-engaged health research at Children's Mercy Hospital in Kansas City.