Children who took midday naps of an average of a little longer than an hour performed better on a task that day and the next day than did the kids who didn't nap, scientists recently in the Proceedings of the National Academy of Sciences.
They also found that the non-nappers couldn't make up the deficit with nighttime sleep.
This is important, the researchers said, in part because there had not been previous research on why napping is important, and as a result, that time was targeted in efforts to find more opportunities for learning because even young children are under pressure for academic achievement.
"With increased curriculum demands and taxpayer pressure, classroom nap opportunities are becoming devalued," the researchers wrote.
These children are in the process of growing from babies who slept off and on all day to children who sleep primarily at night.
"We offer scientific evidence that the midday naps for preschoolers support the academic goals of early education," lead researcher Rebecca Spencer, a research psychologist at the University of Massachusetts Amherst, said in a statement.
The researchers looked at 40 children from six western Massachusetts preschools, ages 3 to 5 ½.
They taught the kids a visual spatial task in the guise of a memory game in which the children were asked to remember where various pictures were located on a grid.
Each child played the game without a nap and after a nap. And they played it the following day. Right after a nap, there wasn't much difference based on the sleeping.
But later in the afternoon, the kids recalled 10 percent more of the picture locations if they had napped than if they had stayed awake. And the benefit remained the next day, the researchers wrote.
The researchers took another group of children, 14 preschoolers, into a sleep lab and assessed them as they napped. The researchers found that the changes in performance were associated with what's called spindle density (a burst of brain activity visible on an EEG).
What they found, they said, may be connected to a process "underlying the stabilization and consolidation of the memory."
Napping should be considered for helping children who have learning delays, the scientists said.
And they concluded, "Although curriculum demands for preschool classrooms are increasing, the benefit of the sleep on learning warrants preservation of the nap opportunity."
Not to mention the break it gives the teachers.
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