A teenager who cannot fall asleep at ten is not being difficult. Their body clock has moved, and school has not

A thirteen-year-old who fell asleep easily at nine o'clock two years ago now lies awake until midnight and cannot be got out of bed at six. The usual reading is a discipline problem — too much phone, too little routine, a generally slackening character. Some of that is real. But underneath it sits a change that is not behavioural at all, is measurable in hormone levels, appears in every population studied and even in other mammals at the equivalent life stage.

At puberty, the circadian clock shifts later. The adolescent is not refusing to sleep at ten. At ten, their body is not yet producing the signal that initiates sleep.

Two processes decide when you fall asleep

Sleep timing is governed by two systems working against each other, and adolescence changes both.

The first is the circadian process, the roughly 24-hour clock in the brain that is entrained by light and drives the evening release of melatonin — the hormone that does not cause sleep so much as announce that biological night has begun. Through adolescence, the timing of that release drifts later, commonly by one to three hours. That is the delayed phase.

The second is homeostatic sleep pressure, which simply accumulates the longer you have been awake. Adolescents build this pressure more slowly than younger children, so the tiredness that would previously have overwhelmed a nine-year-old by nine o'clock does not arrive at the same hour.

Put together: the signal to sleep comes later, and the pressure to sleep builds more slowly. A teenager told to sleep at ten is being asked to do something their physiology is actively working against. Meanwhile, the requirement does not shrink — adolescents need roughly eight to ten hours, about as much as they did before, and arguably at the point in life when they can least afford to miss it.

The collision with the timetable

None of this would matter much if the day started later. It does not. A great many Indian schools begin between seven and eight in the morning, which for a child with a commute means waking at half past five and boarding a bus in the dark. Working backwards from a 7:30 start, sleeping for nine hours requires falling asleep by about nine in the evening — a time at which a fifteen-year-old's melatonin has not yet risen.

The result is chronic, structural sleep restriction: not a bad night, but a deficit accumulated five days a week for years. And because the deficit is created by a schedule rather than by choice, no amount of telling a teenager to sleep earlier resolves it.

Weekends then produce the second half of the pattern. Given freedom, the adolescent sleeps late and wakes late, which is what their clock wants. That means the body is running on one schedule on Saturday and a two-or-three-hour-earlier schedule on Monday — the equivalent of flying across time zones every week, which researchers call social jetlag. Monday morning is not laziness; it is jet lag that nobody travelled for.

Catching up on the weekend helps, and it does not repay the debt. Some of the effects of sleep restriction — on mood, attention and glucose handling — do not fully reverse with two long mornings, and the oscillation itself carries a cost.

What happens when schools move the bell

Because school start time is one of the few variables in this system that can actually be changed, it has been studied directly, and the findings are consistent enough to be worth stating plainly.

Where secondary schools have delayed their start, students sleep longer — not by staying up later, which is the intuitive fear, but by waking later. Bedtime tends to stay roughly where it was, because it is set by the clock rather than by convenience, so the extra half hour or hour of sleep is real. Studies have also reported improvements in attendance and punctuality, better self-reported mood and alertness, and in some settings modest gains in grades, alongside reductions in adolescent road accidents where teenagers drive to school.

Professional bodies in several countries now recommend that secondary schools not begin before about half past eight for exactly this reason.

The honest caveats matter. Most of this evidence comes from high-income settings with different commute patterns and school structures, effect sizes on academic outcomes are modest rather than transformative, and it is difficult to separate a start-time change from everything else a school changes at the same time. The direction of the finding is consistent; the magnitude should not be oversold.

The question is not whether teenagers should sleep more. It is why a timetable designed around adult convenience is treated as fixed while adolescent biology is treated as negotiable.

Sleep is not time taken away from studying

The belief that does the most damage during exam season is that sleep is the slack in the schedule — the thing to cut when there is more to revise.

What happens during sleep argues the opposite. Memory consolidation, the process by which the day's learning is stabilised and integrated into long-term storage, occurs largely during sleep, with different stages contributing to different kinds of memory: slow-wave sleep implicated in factual and declarative learning, REM sleep in procedural skill and in integrating new material with what is already known. Studying material and then not sleeping is, in a real sense, leaving the filing undone.

Sleep deprivation also degrades precisely the functions an examination tests — sustained attention, working memory, the ability to hold a multi-step problem in mind, and emotional regulation under pressure. A student who trades two hours of sleep for two hours of revision is typically buying low-quality revision and paying for it with reduced performance the next day. The all-night study session before a paper is the clearest example of an effort that feels productive and measurably is not.

Why the Indian version is harder than it looks

It would be easy to conclude that schools should simply start later, and in many places that is genuinely the right answer. But the constraints here are not mainly ignorance.

Many Indian schools run double shifts, with one set of students in the morning and another in the afternoon, because the building cannot hold everyone at once. Commutes are long and traffic worsens sharply later in the morning, so an early start is partly a transport decision. Bus fleets are shared between shifts. Summer heat pushes outdoor activity and assembly earlier in the day. Coaching classes, in exam-heavy years, are frequently scheduled before or after school and extend the day at both ends — which for many senior students is the binding constraint rather than the school bell itself.

These are real trade-offs rather than oversights, and they deserve engagement rather than a slogan. But they also mean that the things a family can control — a consistent wake time including weekends, morning light exposure which pulls the clock earlier, keeping the last hour before bed dark and unstimulating, and not treating sleep as the first thing sacrificed to revision — carry more weight here than in places where the timetable is easier to move.

Why it matters for students and researchers

Adolescent sleep is a good example of a field where the biology is settled and the local evidence is thin. Almost all of the influential data comes from Europe, North America and East Asia. India has distinctive conditions that could plausibly change the picture in both directions: later and more variable family bedtimes, multi-generational households with different sleep schedules under one roof, shared sleeping spaces, long commutes, intense coaching schedules, high ambient light and noise, and considerable variation in daylight timing across a country that runs on a single time zone — which means a child in Assam and a child in Gujarat experience very different sunrise times against the same school bell.

The useful studies are tractable. Actigraphy or even well-designed sleep diaries across schools with different start times; measurement of how much of the deficit is school-driven versus coaching-driven; whether interventions on evening light and morning light work in Indian homes; and what happens to sleep across the board-exam year, which is an enormous natural experiment that nobody has properly documented.

That kind of work — the well-being, development and rights of children, across disciplines and settings — is the stated scope of the International Journal of Children (ISSN 3049-1657), a peer-reviewed journal launched in 2024. For students of education, psychology and public health, adolescent sleep is a useful demonstration that a problem widely understood as a failure of character can turn out, on measurement, to be a scheduling conflict.

Frequently asked questions

Why can't teenagers fall asleep early?

Because at puberty the circadian clock shifts later, delaying the evening release of melatonin by one to three hours, and sleep pressure also builds more slowly than in younger children. Both changes push the point at which sleep becomes possible to a later hour.

How much sleep do adolescents need?

Roughly eight to ten hours a night. The requirement does not fall during adolescence, even though the timing of sleep shifts later.

Does sleeping late on weekends fix the problem?

Only partly. Weekend catch-up recovers some of the deficit, but the weekday–weekend swing creates social jetlag, the equivalent of shifting time zones every week, and some effects of chronic restriction do not fully reverse.

Does starting school later just make teenagers stay up later?

The evidence indicates not. Bedtime is set largely by the circadian clock rather than by the following morning's alarm, so when start times are delayed, students mostly wake later and gain sleep.

Is it better to study through the night before an exam?

No. Memory consolidation happens largely during sleep, so material studied and not slept on is poorly retained, and sleep loss directly degrades attention, working memory and emotional regulation — the abilities an exam actually tests.

What can a family do if the school timing cannot change?

Keep wake time consistent including weekends, get bright light in the morning to pull the clock earlier, keep the last hour before bed dim and low-stimulation, and avoid treating sleep as the first thing cut when revision increases.