Schoolyards that feature natural habitat and not just asphalt and recreation equipment reduce children's stress and inattention, according to a recent study.

Researchers from the University of Colorado Boulder found that working on class assignments or gardening in such settings provide stress-reducing benefits for youth. They concluded that natural-terrain schoolyards -- with dirt, scrub oak and water features, for example -- foster supportive relationships and feelings of competence, the researchers found.

Their finding is one of the first to focus on the relationship between student access to green settings and stress.

"Many schools already offer stress management programs, but they're about teaching individuals how to deal with stress instead of creating stress-reducing environments," Louise Chawla, lead author of the study, said in a statement. "Schools are where children spend a major part of their life hours, so it's an important place to look at for integrating daily contact with the natural world because of the many benefits it brings."

For the study, the research team observed a variety of settings including elementary-school students' recess in wooded and built areas; fourth-through sixth-grade students' use of a natural habitat for science and writing lessons; and high school students' gardening for volunteerism, required school service or coursework.

The sites were located at a private elementary school in Baltimore that serves children with dyslexia and other learning disabilities; a public elementary school in suburban Denver with students from a range of socioeconomic backgrounds; and four public and private entities for teenagers -- a college preparatory school, a public high school, an alternative school and an afterschool program -- throughout Colorado.

They logged more than 1,200 hours of observation. They interviewed students, teachers, parents and alumni and coded keywords from the interviews for their findings, among other methods.

For schools that are interested in providing natural habitats for students but only have built outdoor spaces, Chawla suggests tearing out some areas of asphalt or creating joint-use agreements with city parks and open space.

"Schools are really prime sites for an ecological model of health and for building access to nature into part of the school routine as a health measure," Chawla said.

The findings were recently published in the journal Health & Place.