Does physical activity improve student focus?

In spring 2006, obesity researchers at the Mayo Clinic produced an innovative design for the classroom of the future: It has no chairs, uses "standing desks," and incorporates movement into every aspect of classroom activity. The assumption behind the design is that, due to ever-rising rates of obesity and ever-shrinking time for physical education in schools, students benefit -- both physically and academically -- from constant movement during the school day. Proponents of this idea suggest that kids need and want to move, that they can still learn while doing so, and some may even learn better this way. However, constant movement could interfere with classroom structure and distract students from academics. Do you see the benefits, or the drawbacks, of movement in your classroom? We're interested in your opinion.