Although the evidence is telling, few districts have followed this lead. Conversely, 85 percent of America’s public high schools start before 8:15 a.m. Thirty-five percent start at or before 7:30 a.m. In New York City, each school principal sets his own school schedule, and a randomized sample of 50 of the city’s 500 public high schools revealed that 30 percent begin by or before 7:30. At Midwood, class starts at seven on the dot; Van Buren lets you slide in at 7:05.
Obstacles to 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. This 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 class at kickoff time.
Dr. Mark Mahowald, a University of Minnesota professor who runs a sleep clinic, has been at the center of many school start-time debates, and he dismisses those claims. “Of all the arguments I’ve heard over school start-times, not one person has argued that children learn more at 7:15 a.m. than at 8:30.”
Parents and educators might remain skeptical about the importance of the lost hour, but the sleep-research community considers the evidence irrefutable. Their convictions hardened as scientists began to understand sleep’s vital role in synthesizing and storing memories.
Dr. Matthew Walker of UC Berkeley 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 a 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 new words. 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 R.E.M. sleep. The more you learned during the day, the more you need to sleep that night.
To consolidate these memories, certain genes appear to up-regulate 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.
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 get 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 percent of the words with a negative connotation, like cancer. But they could remember only 41 percent of the words with a positive or neutral connotation, like sunshine or basket.
“We have an incendiary situation today,” Walker remarks, “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.”