NurtureShock (5 page)

After the third night’s sleep, a researcher went to the school in the morning to give the children a test of neurobiological
functioning. The test, a computerized version of parts of the Wechsler Intelligence Scale for Children, is highly predictive
of current achievement test scores and how teachers rate a child’s ability to maintain attention in class.

Sadeh knew that his experiment was a big risk. “The last situation I wanted to be in was reporting to my grantors, ‘Well,
I deprived the subjects of only an hour, and there was no measurable effect at all, sorry—but can I have some more money for
my other experiments?’ ”

Sadeh needn’t have worried. The effect was indeed measurable—and sizeable. The performance gap caused by an hour’s difference
in sleep was bigger than the gap between a normal fourth-grader and a normal sixth-grader. Which is another way of saying
that a slightly-sleepy sixth-grader will perform in class like a mere fourth-grader. “A loss of one hour of sleep is equivalent
to [the loss of] two years of cognitive maturation and development,” Sadeh explained.

“Sadeh’s work is an outstanding contribution,” says Penn State’s Dr. Douglas Teti, Professor of Human Development and Family
Studies. His opinion is echoed by Brown’s Dr. Mary Carskadon, a specialist on the biological systems that regulate 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 across all stages. Memories that are emotionally laden get processed during REM sleep. The more
you learned during the day, the more you need to sleep that night.

To reconsolidate these memories, certain genes appear to upregulate during sleep—they literally turn on, or get activated.
One of these genes is essential for synaptic plasticity, the strengthening of neural connections. The brain does synthesize
some memories during the day, but they’re enhanced and concretized during the night—new inferences and associations are drawn,
leading to insights the next day.

Kids’ sleep is qualitatively different than grownups’ sleep because children spend more than 40% of their asleep time in the
slow-wave stage (which is ten times the proportion that older adults spend). This is why a good night’s sleep is so important
for long-term learning of vocabulary words, times tables, historical dates, and all other factual minutiae.

Perhaps most fascinating, the emotional context of a memory affects
where
it gets processed. Negative stimuli get processed by the amygdala; positive or neutral memories gets processed by the hippocampus.
Sleep deprivation hits the hippocampus harder than the amygdala. The result is that sleep-deprived people fail to recall pleasant
memories, yet recall gloomy memories just fine.

In one experiment by Walker, sleep-deprived college students tried to memorize a list of words. They could remember 81% of
the words with a negative connotation, like “cancer.” But they could remember only 31% of the words with a positive or neutral
connotation, like “sunshine” or “basket.”

“We have an incendiary situation today,” Walker remarked, “where the intensity of learning that kids are going through is
so much greater, yet the amount of sleep they get to process that learning is so much less. If these linear trends continue,
the rubber band will soon snap.”

While all kids are impacted by sleep loss, for teenagers, sleep is a special challenge.

Brown’s Mary Carskadon has demonstrated that during puberty, the circadian system—the biological clock—does a “phase shift”
that keeps adolescents up later. In prepubescents and grownups, when it gets dark outside, the brain produces melatonin, which
makes us sleepy. But adolescent brains don’t release melatonin for another 90 minutes. So even if teenagers are in bed at
ten p.m. (which they aren’t), they lie awake, staring at the ceiling.

Awakened at dawn by alarm clocks, teen brains are still releasing melatonin. This pressures them to fall back asleep—either
in first period at school or, more dangerously, during the drive to school. Which is one of the reasons young adults are responsible
for more than half of the 100,000 “fall asleep” crashes annually.

Persuaded by this research, a few school districts around the nation decided to push back the time school starts in the morning.

The best known of these is Edina, Minnesota, an affluent suburb of Minneapolis, which changed its high school start times
from 7:25 to 8:30. The results were startling, and it affected the brightest kids the most. In the year preceding the time
change, math/verbal SAT scores for the top 10% of Edina’s 1,600 students averaged 683/605. A year later, the top 10% averaged
739/761. In case you’re too drowsy to do that math, getting another hour of sleep boosted math SAT scores of Edina’s Best
and Brightest up 56 points, and their verbal SAT score a whopping 156 points. (“Truly flabbergasting,” gasped a stunned and
disbelieving Brian O’Reilly, the College Board’s Executive Director for SAT Program Relations, when he heard the results.)
And the students reported higher levels of motivation and lower levels of depression. In short, an hour more of sleep improved
students’ quality of life.

That’s particularly remarkable since most kids get less sleep during high school, and their quality of life goes down: University
of Kentucky’s Danner has studied how, on a national level, sleep decreases each year during high school. In their first year,
60% of kids got at least eight hours on average. By the second year, that was down to 30%. Right alongside this decline went
their moods; dropping below eight hours doubled the rate of
clinical-level
depression. Over one-eighth of the students reached this classification, which makes one only wonder how many more suffer
from melancholy of a lesser degree.

Another trailblazing school district is Lexington, Kentucky, which also moved its start time an hour later. Danner has been
studying the before/after equation. The finding that most jumps out from his data is that after the time change, teenage car
accidents in Lexington were down 25%, compared to the rest of the state.

While the evidence is compelling, few districts have followed this lead. Conversely, 85% of America’s public high schools
start before 8:15 a.m., and 35% start at or before 7:30 a.m.

Obstacles against later start times are numerous. Having high schools start earlier often allows buses to first deliver the
older students, then do a second run with the younger children. So starting later could mean doubling the size of the bus
fleet. Teachers prefer driving to school before other commuters clog the roads. Coaches worry their student-athletes will
miss games because they’re still in their class at kickoff time. Many simply aren’t persuaded by the science. When Westchester
schools declined an initiative to start high schools later, then-superintendent Dr. Karen McCarthy opined, “There’s still
something that doesn’t click for me.”

Dr. Mark Mahowald has heard all those arguments. As Director of the Minnesota Regional Sleep Disorders Center, he’s been at
the center of many school start time debates. But of all the arguments he’s heard, no one’s argument is that children
learn more
at 7:15 a.m. than at 8:30. Instead, he forcefully reasons, schools are scheduled for adult convenience: there’s no educational
reason we start schools as early as we do. “If schools are for education, then we should promote learning instead of interfere
with it,” he challenges.

“We thought the evidence was staggering,” Carole Young-Kleinfeld recalled.

Kleinfeld is a mother in Wilton, Connecticut, thirty miles up I-95 from New York City. Wilton, too, had saved money by running
buses in two shifts, starting the high school at 7:35. Then a few years ago, Kleinfeld was at a meeting for the local League
of Women Voters. Then-state senator Kevin Sullivan spoke about Carskadon and others’ research, and how starting high school
at a more reasonable hour was the answer.

Kleinfeld had a sullen teenager of her own, and when she went to local high schools to register kids to vote, she regularly
saw students sleeping in the halls during class. So the idea hit home. She and others formed a committee to learn about the
issue. Eventually, they convinced the district to move the high school’s start time to 8:20.

For Kleinfeld, the change “was a godsend.”

Her son Zach had once been a perfectly happy kid, but when he hit high school he became the prototypical disengaged, unenthralled-by-everything
teen. He was so negative, so withdrawn that “I really thought we’d lost him,” Kleinfeld sighed. “We’d lost that sense of connection.”