"Green schoolyards can include outdoor classrooms, native gardens, storm water capture, traditional play equipment, vegetable gardens, trails, trees and more," Dr. Stephen Pont said in an American Academy of Pediatrics news release.

He and his colleagues found that green schoolyards provide benefits in areas such as heart health, weight control, attention-deficit/hyperactivity disorder (ADHD) and stress relief.

"And outside of school time, these schoolyards can be open for the surrounding community to use, benefitting everyone," added Pont, medical director of the Texas Center for the Prevention and Treatment of Childhood Obesity.

For their report, Pont's team summarized the findings of prior published studies on the potential benefits of green schoolyards.

"We should all be champions for kids and families getting more Vitamin N," he urged, referring to nature.

Richard Louv is another advocate for outdoor time in childhood.

"Too many children have no access to quality school grounds. In many neighborhoods, the standard play space is a barren asphalt playground or a concrete slab surrounded by chain link fence -- a completely unsuitable environment for children's play," said Louv, co-founder of the Minneapolis-based Children & Nature Network.

The group has collaborated with the National League of Cities and helped these five cities implement green schoolyards: Austin, Texas; Grand Rapids, Mich.; San Francisco, Calif.; Providence, R.I.; and Madison, Wis.

"So many physicians and health professionals choose to spend their free time in nature, but we often forget that nature can be a powerful health intervention for our patients, both for the prevention and improvement of many medical conditions," Pont said.

The study findings were presented this weekend at the American Academy of Pediatrics national meeting in Chicago. Research presented at meetings is usually considered preliminary until published in a peer-reviewed medical journal.