When Deborah Gilboa's second-oldest son Nadav started coming home from first grade with discipline warnings from his teacher, Gilboa and her husband were perplexed.
Nadav, who had just turned 6, had the same teacher in kindergarten and had rarely gotten into trouble.
So Gilboa, a medicine doctor in Pittsburgh who consults at Deborahgilboamd.com, and her husband sat down to ask their son what was going on. He had the answer right away.
"He said, 'In kindergarten we had recess twice a day and we went to gym twice a week,'" Gilboa told LiveScience. Now, as a first-grader, Nadav's class only went to gym once every six days.
They had one recess period a day, split with lunch, so that Nadav had only about 15 minutes a day to run around.
"He said, 'I get this feeling in my legs when they want to run and that feeling moves up to my belly and when that feeling moves up to my head I can't remember what the rules are," Gilboa said. "So he had really noticed a big change in his own behaviour and self-control."
For children like Nadav, the transition from summer freedom to the grindstone of the classroom may be tough. With schools under pressure to meet standardised testing goals, recess has been cut back and even eliminated in some school districts.
The irony, experts say, is that schools may be shooting themselves in the foot by taking away playtime that's crucial to a child's growth.