Well.....Duh?

More recess and play helps to improve productivity:

But ask the adults and they'll tell you it's because Eagle Mountain is part of a project in which the school day is modeled after the Finnish school system, which consistently scores at or near the top in international education rankings. The project's designer is Texas Christian University kinesiologist Debbie Rhea.
"I went over there to find out where they've come in the last 20 to 25 years. Yes, their test scores are good, but they are also healthy in many regards," she says.
The biggest difference Rhea noticed was that students in Finland get much more recess than American kids do. "So, I came back with the idea to bring recess back to the schools. Not just one recess, but multiple recesses."

Read (or listen) at NPR.