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Good sleep habits correspond to academic success. The link between hitting the sack and scoring A's bears out in grade school, graduate school and everywhere in between. This general trend shouldn’t be surprising, given that the well-rested display a host of skills and behavioral tendencies relevant to classroom domination. Compared to sleep-starved people, they exhibit faster reaction times, sharper recollection, heightened focusing abilities and a higher threshold for working under stress. Here are seven interesting takeaways from research on students young and old(er).

1. For little kids, a little more sleep helps

A new McGill University study showed that kids (ages 7-11) who increased their nightly rest by 18 minutes (on average) for five nights showed considerable improvements on their report cards. Why would 7 year olds be underslept (given that they have externally imposed bedtimes and few or no responsibilities)? Well, even fun-sized humans undergo lifestyle changes. One 2014 study identified kindergarten as a sleep-health turning point. Kindergarten, and the loss of napping that comes with it, corresponded to less overall weekday sleep and earlier weekday bedtimes, particularly for kids who hadn’t gone to preschool. (Hey, universal preschool.)

2. Snoring sets students back

A lot of research on younger students’ sleep concerns sleep apnea. The condition, marked by shallow breathing and snoring, results in less, more-fragmented sleep. Children who have obesity and live in low-income households are at a considerably heightened risk for sleep-breathing disorders. And they tend to fare poorly in school, both during primary school and afterwards. Going back to 2001, a study found that 13 and 14 year olds who struggled in school were more likely to have snored when they were younger. By extension, kids from lower-income families fall behind in school. Seems pretty fair.

3. Early(ish) bedtimes yield higher GPAs

A large population survey in Norway showed that teens ages 15 to 19 who went to bed between 10p.m. and 1a.m. had the highest GPAs. Getting too little sleep increased students’ odds of having GPAs in the lowest quartile. It’s easy to use these sorts of findings to admonish teens for staying up too late. But teens are naturally night owls, at least according to the leading research. Their circadian clocks are shifted, making it especially hard for adolescents to keep early hours.

4. Experts really, really support later school start times

The campaign for later school start times is heavily rooted in the misalignment between teens' biological clocks and their externally imposed schedules. The big idea? Let kids learn when they're best-equipped to soak up and retain knowledge. Not to mention, forcing teenage night owls to rise at dawn robs them of Zzzs that set them up for academic success, support their cognitive and emotional development and protect their mental and physical health. The American Academy of Pediatrics recommends that schools start no earlier than 8:30a.m. And, in general, experts are all in on pushing back start times. 

The benefits of later start times aren't confined to teens: According to a recent report from the RAND Corporation, delaying the morning bell would save the US about $9 billion a year. These projected economic gains are primarily due, according to the report, to the impact of improved academic performance on future earnings and the reduction in car accidents caused by tired teens.

Researchers speculated that device use only further threw off teens’ circadian rhythms. Weird bodies, bad habits, can’t win.

But, despite the strong case for later start times, only about 15 percent of public schools across the country actually kick off the school day at or after 8:30, based on a 2016 survey of US principals. Why? Schools claim that postponing start times is too logistically difficult and expensive. And, in a study from The University of Michigan, only about half of parents supported later start times. But there are plenty of impassioned people involved in the campaign, so don't expect the conversation around school start times to die down anytime soon.  

5. Body clocks and bad habits are a dangerous pair  

A number of studies have linked Delayed Sleep Phase (a preference for keeping especially late hours) to lower academic performance. But, in several instances, researchers found another factor underlying the link. In one case, that factor was school attendance — students with DSP did worse in school, perhaps because they missed a lot of it. Would they show up if first period started later? Advocates for bumping back first period would probably say yes.

But, in other cases, research says low grades have more to do with teens' habits than their wonky bodies. The big culprits: caffeine consumption and late-night electronic use. All other factors aside, coffee drinkers and bedtime Snapchatters got less sleep and lower grades in one 2015 study. Even students who said they used TV and music for the express purpose of falling asleep carried out the trend. Researchers speculated that device use only further threw off teens’ circadian rhythms. Weird bodies, bad habits, can’t win.

6. Sleeping efficiently helps students score well

We can assess sleep using a number of measures. One such measure is sleep efficiency, the proportion of time in bed that people actually spend sleeping. (To calculate sleep efficiency, divide hours in bed by hours slept.) In one 2015 Italian study, sleep efficiency emerged as a key predictor of exam grades for students in their final year of high school. Researchers did not find a significant relationship between exam grades and other sleep measures, including total duration of sleep (amount of sleep logged, efficiency notwithstanding) and sleep midpoint (also called mid-sleep time). Here’s the formula for calculating sleep midpoint:

  • Take the average number of hours you sleep each night and divide that number in half. Add that number to your average bedtime on free days (meaning days on which work or school do not define your schedule). That’s your midpoint. So, if I sleep seven hours, and I go to bed at midnight, my midpoint is: 3:30 a.m. (that's 3.5 + 12).

7. Med school students are hard to predict

But MDs-in-training still perform better when they have healthy sleep habits. One study from Munich found a link between sleep duration and final-exam performance. But, so long as students got enough sleep, they fared okay. Neither chronotype (e.g., morning lark or evening owl) nor self-reported sleep quality appeared to affect students’ scores.

Another study on Sudanese med students found a significant difference in duration and quality of sleep between excellent and merely satisfactory students. On average, snoring afflicted 9 percent of the gunners, who averaged seven hours of sleep each night. By comparison, 28 percent of the hangers-on snored, and they only logged 6.3 hours of rest each night.

And a third study (med student sleep is well-documented) found, somewhat counter-intuitively, that “it is not the generally poor sleepers who perform worse in the medical board exams.” Students who slept poorly immediately before taking exams (during study periods) were most likely to choke, but those who struggled with sleep over the course of the semester still managed to crush it. 

This story was originally published in 2016. It has been updated since then.