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In a TED talk "Why school should start later for teens", Wendy Toxel made an assertion that teenagers naturally fall asleep and rise up a couple of hours later than children OR adults (related to Melatonin production time).

I found one BBC article agreeing, but it didn't cite any research.

Does the research conclusively back that assertion up?

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    Unspoken: "Or are they just lazy?"
    – Ask About Monica
    Commented May 24, 2017 at 23:52
  • I'd also like to see how this lines up to the many, MANY articles about training your own circadian rhythm. Are teenagers unable to decide when they sleep?
    – AJFaraday
    Commented May 25, 2017 at 8:28
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    When I first started a job where I got to set my own hours, I quickly fell back to the "teenage sleep cycle" and felt I was actually more productive for it. I have to wonder how much of the "adult" sleep cycle is just a constraint of having to hold down a job.
    – Chuu
    Commented May 25, 2017 at 16:26
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    @kbelder - if all teenagers are universally lazy, that too must be biological.
    – Davor
    Commented May 25, 2017 at 16:54
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    Personally I don't feel like getting up late is a privilege of teenagers only. I'm 36 and the only reason I wake up early is because of my 4 year old daughter.
    – Markus Malkusch
    Commented May 26, 2017 at 10:04

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There does appear to be fairly solid research backing this claim.

A summary page from UCLA: Sleep and Teens

One change in the body during puberty is closely related to how you sleep. There is a shift in the timing of your circadian rhythms. Before puberty, your body makes you sleepy around 8:00 or 9:00 pm. When puberty begins, this rhythm shifts a couple hours later. Now, your body tells you to go to sleep around 10:00 or 11:00 pm.

Neurology Times agrees:

In turns out that adolescents have a delayed release of regular daily melatonin, which causes them to become sleepy later at night, hours after nightfall. Given the fact that teenagers have an established need for 8-10 hours of sleep per night, the delayed melatonin release that allows teenagers to fall asleep late in the day has the expected effect of predisposing them to remain asleep for longer into the late morning or early afternoon, when it is feasible.

A relevant reference for the Neurology Times article:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2820578/

Other studies have been done that suggest better outcomes in teenage students when school starts later in the day, and not just in school:

Later high school start times are associated with positive outcomes among teens, including longer weekday sleep durations and reduced vehicular accident rates, research suggests.

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    I've always been skeptical of these studies, because its rare that they show or explore any mechanism connecting the two. The only thing I can think of is the Sun. So, what happens in areas with Daylight Savings time vs. areas that don't have it? Are the same effects seen at higher latitudes where the period of sunlight is lessened in the Winter? How about areas that are cloudy a lot of the year? They all seem to want to imply some magic relationship between health and the arbitrary numbers we assigned to timekeeping devices 4 millennia ago.
    – T.E.D.
    Commented May 24, 2017 at 20:18
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    @sgroves It would help us determine whether it's something biological and inherent that can't be changed, or if it's something to do with our modern lifestyle that could be modified or ameliorated if we felt the need.
    – Werrf
    Commented May 24, 2017 at 22:36
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    @sgroves It's not about getting everyone on the planet to adjust, it's about having the information to make an informed choice. We know that smoking can cause cancer. It's something to consider when making a choice. If my teenage son is struggling in school because he's short of sleep, I'd like to know if I can help him by cutting off video games sooner in the evening or by changing the lightbulbs, or if I should pressure the school into letting him start later in the day because there's nothing that can chance his sleep patterns.
    – Werrf
    Commented May 25, 2017 at 11:55
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    @T.E.D: studies are experimental, they're measuring what happens. So if indeed "adolescents have a delayed release of regular daily melatonin", that continues regardless of whether or not we can figure out how their pineal gland "knows" what time it is (but, yes, light has a lot to do with that). Rejecting experimental results because the experimentalist hasn't provided a complete theory seems... wrong. On the other hand, rejecting an alleged theory because it fails to propose a mechanism would be right.
    – Steve Jessop
    Commented May 25, 2017 at 14:30
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    @T.E.D.: to be fair to the school, even if the late melatonin-release turns out to be localised to Western teenagers making poor choices about when they go to bed, that fail to take into account their higher need for sleep compared with adults, then it still might be a rational response for the school to change hours. "We've tried asking you to send your kids to bed on time, studies show that didn't work and their melatonin release is too late, this is the next step". The school doesn't need to care why all their pupils are still asleep at 9am, just accept they've failed to prevent it :-)
    – Steve Jessop
    Commented May 25, 2017 at 14:42

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