(NBC NEWS) -- Students may need to break a typical school rule: Get up from their desks and give in to their natural impulse to move around.
The Institute of Medicine is recommending that schools provide students with an hour of exercise every day, not just for health but for the sake of their grades.
"Children need physical activity to optimize health, development. And we're finding now for academic performance," explains Dr. Harold Kohl of the University of Texas School of Public Health.
The "No Child Left Behind Act" passed in 2001 put a greater emphasis on math and reading.
As a result 44-percent of school principals say they've cut back on physical education, but according to the Institute of Medicine grades haven't improved.
The solution, experts say, is to put physical activity back in schools.
"Any time there's a class after P.E., phys-ed, the kids are more on task, and they're more focused. That's a good thing," says middle school principal Dr. Allyn Bernstein.
Gym class isn't the only answer.
The experts are calling for a "whole school" approach to get kids moving. This includes teaching teachers how to incorporate physical activity into math, science and English classes.
"We need to think creatively about active transport to school -- walking, biking, skateboarding to and from school," Dr. Kohl says. "We need to think about recess, before- and after-school activities, sports."
Their health, and increasingly their grades, depend on it.
The recommendations have some support in congress.
On Thursday several members introduced legislation that would amend the "No Child Left Behind Act" to include more physical activity.