Kirsten Luce for The New York Times SWITCHED Children playing before lunch at Sharon Elementary School in Robbinsville, N.J. “Kids are calmer after they’ve had recess first,” the school’s principal said. Kirsten Luce for The New York Times

Can something as simple as the timing of recess make a difference in a child’s health and behavior?

Some experts think it can, and now some schools are rescheduling recess — sending students out to play before they sit down for lunch. The switch appears to have led to some surprising changes in both cafeteria and classroom.

Schools that have tried it report that when children play before lunch, there is less food waste and higher consumption of milk, fruit and vegetables. And some teachers say there are fewer behavior problems.

“Kids are calmer after they’ve had recess first,” said Janet Sinkewicz, principal of Sharon Elementary School in Robbinsville, N.J., which made the change last fall. “They feel like they have more time to eat and they don’t have to rush.”

One recent weekday at Sharon, I watched as gaggles of second graders chased one another around the playground and climbed on monkey bars. When the whistle blew, the bustling playground emptied almost instantly, and the children lined up to drop off their coats and mittens and file quietly into the cafeteria for lunch.

“All the wiggles are out,” Ms. Sinkewicz said.

One of the earliest schools to adopt the idea was North Ranch Elementary in Scottsdale, Ariz. About nine years ago, the school nurse suggested the change, and the school conducted a pilot study, tracking food waste and visits to the nurse along with anecdotal reports on student behavior.

By the end of the year, nurse visits had dropped 40 percent, with fewer headaches and stomachaches. One child told school workers that he was happy he didn’t throw up anymore at recess.

Other children had been rushing through lunch to get to the playground sooner, leaving much uneaten. After the switch, food waste declined and children were less likely to become hungry or feel sick later in the day. And to the surprise of school officials, moving recess before lunch ended up adding about 15 minutes of classroom instruction.

In the Arizona heat, “kids needed a cool-down period before they could start academic work,” said the principal, Sarah Hartley.

“We saved 15 minutes every day,” Dr. Hartley continued, “because kids could play, then go into the cafeteria and eat and cool down, and come back to the classroom and start academic work immediately.”

Since that pilot program, 18 of the district’s 31 schools have adopted “recess before lunch.”

The switch did pose some challenges. Because children were coming straight from the playground, the school had to install hand sanitizers in the lunchroom. And until the lunch system was computerized, the school had to distribute children’s lunch cards as they returned from recess.

In Montana, state school officials were looking for ways to improve children’s eating habits and physical activity, and conducted a four-school pilot study of “recess before lunch” in 2002. According to a report from the Montana Team Nutrition program, children who played before lunch wasted less food, drank more milk and asked for more water. And as in Arizona, students were calmer when they returned to classrooms, resulting in about 10 minutes of extra teaching time.

One challenge of the program was teaching children to eat slower. In the past, children often finished lunch in five minutes so they could get to recess. With the scheduling change, cafeteria workers had to encourage them to slow down, chew their food and use all the available time to finish their lunch.

Today, about one-third of Montana schools have adopted “recess before lunch,” and state officials say more schools are being encouraged. “The pilot projects that are going on have been demonstrating that students are wasting less food, they have a more relaxed eating environment and improved behavior because they’re not rushing to get outside,” said Denise Juneau, superintendent of the Office of Public Instruction. “It’s something our office will promote to schools across the state as a best practice.”

Children’s health experts note that such a switch might not work in many urban school districts, where lower-income children may start the day hungry.

“It’s a great idea, but first we’ve got to give them a decent breakfast,” said Dr. David Ludwig, director of the obesity program at Children’s Hospital Boston. “A lot of kids skip breakfast and arrive at lunch ravenous.”

And for a seemingly simple scheduling change, it can create some daunting logistical problems. Children often have to return to hallways and classrooms after recess for bathroom breaks and hand washing and to pick up lunch bags. The North Ranch Elementary School regularly fields calls from schools in colder climates with questions on how to deal with coats, hats, galoshes and mittens. “In Arizona, we don’t have to deal with that,” said Dr. Hartley, the principal.

Many school districts say such problems make them reluctant to switch. A 2006 study in The Journal of Childhood Nutrition & Management reported that fewer than 5 percent of the nation’s elementary schools were scheduling recess before lunch.

But at the Sharon Elementary School, the principal, Ms. Sinkewicz, says the challenges have been worth it. In the past, children took coats, hats and mittens with them to the lunchroom, then headed outside. Now they have time to return coats to lockers so they don’t have to carry them to the lunchroom.

“For some reason, kids aren’t losing things outside,” Ms. Sinkewicz said. “The lost-and-found mound has gone down.”