Chicago schoolkids are going out for recess this week for the first time in 30 years — the mayor added time to the very short school day — and principals are worried that children don’t know how to play, reports the Chicago Tribune.

When Chicago’s Bright Elementary School added 15 minutes of recess to its school day this year, teachers ventured outdoors to find a run-down schoolyard with no playground, a sometimes violent neighborhood and a generation of kids who didn’t know how to play outside.

At Namaste Charter School, officials this year spent $23,000 for a “recess coach,” a modern-day schoolyard referee tasked with keeping fights and bullying to a minimum while also teaching games that could be unfamiliar to today’s schoolchildren — games like four square, tag and dodgeball.

Recess helps children learn, writes Nicholas Day in Slate.

Repeated studies have shown that when recess is delayed, children pay less and less attention. They are more focused on days when they have recess. A major study in Pediatrics found that children with more than 15 minutes of recess a day were far better behaved in class than children who had shorter recess breaks or none at all.

They’ll get more out of class, too: Children seem to learn more efficiently when information is spaced out—when it is distributed over time. It’s been widely documented that the brain needs a break. High-performing East Asian schools have famously long school days—but much of the extra time is taken up by recess, not instruction.

But principals see recess as a time of chaos. So the new recess is “more structured and sports-focused, less dreamy and aimless.”

The nonprofit organization Playworks puts full-time “recess coaches” in low-income schools—currently they’re in 387 schools in 23 cities—who teach children how to play: They organize games; they model how to resolve disputes (rock-paper-scissors); they try to get kids more active and engaged.

Playworks claims to add only the structure that might be provided by a big brother or sister teaching the little kids how to set up a game. There’s little fighting or bullying, the group says. But will the little kids grow up to run their own games?

Recess is a “no-brainer,” says Anthony Pellegrini, a professor of educational psychology at the University of Minnesota. But it’s value is undercut when the kids aren’t in charge.

 “A very important part of what kids do on the playground is social competence—that is, they learn how to get along with others,” he says. “You have to cooperate, you have to use language, you have to compromise. And that’s not trivial. That is huge, in terms of both academic success and success in life.”

Low-income children are the most likely to live in places where it’s not safe to play outside. They’re also the least likely to have time for play at school. “The more minority students a school has, and the lower the income level of their parents, the less time allotted for recess—nearly half of poor children go all day without it,” writes Day.