Here's a link to one study done with school age children and treadmills: Physical Activity May Strengthen Children's Ability To Pay Attention. (This was not the one I was looking for originally, I think there is one other study out there somewhere that looked at eighth graders, but can't find it. Anyone?)
The authors three recomendations:
- scheduling outdoor recess as a part of each school day;
- offering formal physical education 150 minutes per week at the elementary level, 225 minutes at the secondary level;
- encouraging classroom teachers to integrate physical activity into learning.
[Image captured from Instructables: http://www.instructables.com/id/Treadmill-Desk/]