The Globe and Mail

But over the past decade, 100 schools have added trees, shrubs and gardens to their grounds. Dr. Kuo has been able to track whether the greenery is linked to an improvement in test scores in schools at which the demographics have remained the same.

“The initial findings look promising,” she said.

Yale University’s Stephen Kellert said it is smart to focus on practical fixes, like making school yards and back yards more enticing for children. But indoor spaces should also be rethought, he said, since people spend 90 per cent of their lives inside. Natural light, ventilation and other design elements may also help youngsters perform better.

At the Coombes school, the students range in age from 3 to 11 and spend about half of their time outside over the course of the school year.

Cam Collyer said that when he visited two years ago, his North American sensibilities were shocked by all the small nooks and crannies where children could find private spaces. He was also impressed by the poetic way Ms. Humphries was able to describe why it is so important to create a sense of the wild for every child. Mr. Collyer directs the school-ground greening program at Evergreen, a national charity in Canada. He invited Ms. Humphries to speak at All Hands in the Dirt, a forum on the topic being held this weekend in Toronto.

“She is an unlikely celebrity,” he said. “But Coombes is arguably one of the best designed school grounds in the world.”

Mr. Collyer credits the growing awareness of the need to get children out of doors to Last Child in the Woods a book by U.S. author Richard Louv, who coined the phrase “nature deficit disorder” to describe the disconnect between today’s indoor children and the natural world. Published in 2005, it tapped into the unease many parents feel about the lack of unstructured time children have to explore the outdoors, especially compared to their own childhoods. Mr. Louv is the co-founder and chairman of Children & Nature Network, which works to connect children with nature.

That’s Ms. Humphries’s mission as well, one she argues is more important than how children score on standardized tests. The Coombes school does about average, but that, she said, is not the point. She knows how well her students respond to learning out of doors, especially boys, who many people feel are being short-changed in modern classrooms.

Now retired from teaching, Ms. Humphries has travelled to Japan, Sweden, Norway and the Netherlands to offer practical advice on how to rip up asphalt and create inviting landscapes even in small school yards.

“It is important to raise children with other species, with fruits, flowers and gardens so they can plant and grow and understand something about the cycle of nature. ...We owe the world this as well as the children.”