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sleep.
     “Sadeh’s research is an important reminder of how fragile children are.”
    Sadeh’s findings are consistent with a number of other researchers’ work—all of which points to the large academic consequences
     of small sleep differences. Dr. Monique LeBourgeois, also at Brown, studies how sleep affects prekindergartners. Virtually
     all young children are allowed to stay up later on weekends. They don’t get less sleep, and they’re not sleep deprived—they
     merely shift their sleep to later at night on Fridays and Saturdays. Yet she’s discovered that the sleep shift factor alone
     is correlated with performance on a standardized IQ test. Every hour of weekend shift costs a child seven points on the test.
     Dr. Paul Suratt at the University of Virginia studied the impact of sleep problems on vocabulary test scores taken by elementary
     school students. He also found a seven-point reduction in scores. Seven points, Suratt notes, is significant: “Sleep disorders
     can impair children’s IQ as much as lead exposure.”
    If these findings are accurate, then it should add up over the long term: we should expect to see a correlation between sleep
     and school grades. Every study done shows this connection—from a study of second- and third-graders in Chappaqua, New York,
     up to a study of eighth-graders in Chicago.
    These correlations really spike in high school, because that’s when there’s a steep drop-off in kids’ sleep. University of
     Minnesota’s Dr. Kyla Wahlstrom surveyed over 7,000 high schoolers in Minnesota about their sleep habits and grades. Teens
     who received A’s averaged about fifteen more minutes sleep than the B students, who in turn averaged fifteen more minutes
     than the C’s, and so on. Wahlstrom’s data was an almost perfect replication of results from an earlier study of over 3,000
     Rhode Island high schoolers by Brown’s Carskadon. Certainly, these are averages, but the consistency of the two studies stands
     out. Every fifteen minutes counts.

    With the benefit of functional MRI scans, researchers are now starting to understand exactly how sleep loss impairs a child’s
     brain. Tired children can’t remember what they just learned, for instance, because neurons lose their plasticity, becoming
     incapable of forming the new synaptic connections necessary to encode a memory.
    A different mechanism causes children to be inattentive in class. Sleep loss debilitates the body’s ability to extract glucose
     from the bloodstream. Without this stream of basic energy, one part of the brain suffers more than the rest—the prefrontal
     cortex, which is responsible for what’s called “Executive Function.” Among these executive functions are the orchestration
     of thoughts to fulfill a goal, prediction of outcomes, and perceiving consequences of actions. So tired people have difficulty
     with impulse control, and their abstract goals like studying take a back seat to more entertaining diversions. A tired brain
     perseverates—it gets stuck on a wrong answer and can’t come up with a more creative solution, repeatedly returning to the
     same answer it already knows is erroneous.
    Both those mechanisms weaken a child’s capacity to learn during the day. But the most exciting science concerns what the brain
     is up to, when a child is asleep at night. UC Berkeley’s Dr. Matthew Walker explains that during sleep, the brain shifts what
     it learned that day to more efficient storage regions of the brain. Each stage of sleep plays its own unique role in capturing
     memories. For example, studying a foreign language requires learning vocabulary, auditory memory of new sounds, and motor
     skills to correctly enunciate the new word. The vocabulary is synthesized by the hippocampus early in the night during “slow-wave
     sleep,” a deep slumber without dreams. The motor skills of enunciation are processed during stage 2 non-REM sleep, and the
     auditory memories are encoded