School Start Time: City Boys Matter!

Is a later school start time better for teenagers?

“Yes, of course”, you say! But how do you know that?

What if I told you that the correct answer is  “It depends”?

Does School Start Time Matter?

To answer this question, investigators at the National Institutes of Mental Health (NIMH) sent surveys to high school students, aged 13-17, all over the US. Almost 10,000 kids participated.

NIMH investigators asked questions about bedtimes, amount of sleep, and various other questions to tease out important demographic information. Weeknight bedtime was assessed with the question “What time do you usually go to bed on weeknights?” Sleep duration was assessed with the question “How many hours of sleep do you usually get on week (weekend) nights?” They asked this question to indicate whether the teenagers slept at least 8.5 hours of sleep. This number was chosen, instead of 9.5 hours, as is currently recommended, because at the time of the study, the National Sleep Foundation (NSF) recommended only 8.5 hours for teens.

Any high school kid will tell you that it’s much more complicated to understand the truth about their sleep. For this reason, the NIMH investigators asked about family characteristics, after-school jobs and extracurriculars. They also asked about school type (public vs. private, etc) and grade level.

Here’s What They Found

The NIMH school start time study is a good example of why it’s never a good idea to assume you know the answer to a question. Always investigate.

Need a SLEEP COACH?

The results were surprising. Investigators found some results they expected, but many others they did not expect.school start time 2

Teenagers Don’t Sleep Enough

The average number of weeknight sleep hours was 7.71 hours (7.60 for girls and 7.81 for boys). Not only was this result almost an hour less than the recommended NSF nightly allowance, it was almost two hours less than current recommendations!

But as this number was an average, it is obvious that some teenagers slept less than 7.71 hours, and some slept more. Extra sleep was associated with some surprising findings, which we’ll get to soon.

When school started later, students went to bed later. This was one of the expected findings.  And here is where it gets interesting.

School Start Time Matters… Until 8 AM

The investigators looked at school start times and then asked how many students got adequate sleep at each starting hour (e.g., 6:30 AM, 7:00 AM, etc.) When school started later, students got more sleep and more got the recommended amount of sleep (8.5 hours), but the effect went away for start times after 8:00 AM. In other words, if school started at 8:30 AM, or 9:00 AM, the students on average did not get more sleep! There appeared to be “diminishing returns”. In other words, later school start times was good for high schooler’s sleep… up to a point, namely 8:00 AM.

It Gets More Complicated…

It turns out that the benefits of later school start times may fall to boys only. When investigators looked at boys and girls separately, they found some unexpected results. School start time was not associated with hours of sleep for girls, regardless of start time. Similarly, later start times did not correlate with girls getting their 8.5 hours of sleep. School start time just didn’t seem to have anything to do at all with girl’s sleep. school start time 3

What about the boys? Since girls’ sleep didn’t seem to be affected by school start time, you would think that when you removed girls from the analysis that the effect would be even bigger for boys.

And it was… up to a point.

When school started later, boys got more sleep, and more boys got “adequate sleep” but the effect went away after 8AM.

City Boys vs. Country Boys

It turns out that location of the school mattered quite a bit. Investigators divided the kids into three groups: major metropolitan county (census-defined metropolitan counties with ≥ 1 million residents), other urbanized county (metropolitan counties with < 1 million residents), and non-urban county (non-metropolitan counties).

For boys living in major metropolitan areas, later start time was associated with adequate sleep, but only until 8 AM. For boys living in “other urbanized counties” and non-urban counties, start time had no effect on adequate sleep. Put another way, for boys going to big-city schools, later start times were associated with better sleep (up until 8 AM, of course…) For boys in smaller cities or suburbs, start time appeared to have no effect on quality sleep.school start time 4

Once again, girls sleep was unaffected by location. City girls got just as much sleep as country girls.

Make-up Sleep

In an earlier post, we showed that teenagers tend to sleep differently on weekends. These are the days we expect teenagers to “make-up” on sleep.

It is reasonable to guess that the teens who go to high schools with later start times might not need to make up for lost sleep on weekends. Indeed this is what the NIMH investigators found at first… until they “adjusted” the results. “Adjustment” means eliminating or reducing the confounding effects of extraneous confounding factors like sex, age, etc. The NIMH investigators adjusted data for all their results in this study, but when they used adjustment to look at make-up sleep, they got an unexpected result:

There seemed to be a correlation between later start times and less make-up sleep, but the effect would go away after normalizing for age, sex, school level, and school location (city vs. country, etc). In other words, overall later school start time did not give teenagers the opportunity to make up for lost sleep.

Strengths of the Study

Large studies are always better than small studies. The statistics always get better for one thing. Put another way, you can resolve small differences, and bring out subtleties better if your study has more subjects. We believe something closer to the truth is found when you look at very large populations. Almost 10,000 high school kids is a large enough sample size to give results we can believe. And indeed this study found some interesting differences: between boys and girls, and between city boys and country boys.school start time 5

The large sample size also allowed the NIMH investigators to uncover the compelling finding about the hour of 8:00 AM: Later start times did indeed matter, but the effect would disappear after 8.

Limitations of the Study

Survey results are never the best way to arrive at the truth. Think of those times in American history when opinion polls grossly mis-calculate the outcomes of elections! The NIMH school start time study was limited by use of a cross-sectional survey as the research tool. As a result, all the investigators could tell us is that there were associations between things like school start times and hours of sleep. They were unable to tell us if any two things were causally related to each other.

Furthermore, it’s far more accurate to measure hours of sleep than it is to ask a teenager how long she slept! In a study this large, actual measurement was not possible. They also did not ask the kids about confounders like cell phone use, which may vary from group to group.

Finally, there is the question of generalizability. It is important, when reading about studies like this on the internet, to ask an important question: “Does this study apply to me?”  If this same study were performed on teenagers living in isolated villages deep in the Amazon River basin, you might justifiably say “I’m not sure this study tells me anything about my teenager’s sleep”. But you can still ask the question about studies done on American teenagers. Look carefully at the study and ask yourself how easily your child could have been one of the kids who turned in a survey.

Summary: The NIMH School Start Time Study Suggests…

  • That teenagers don’t get enough sleep
  • That later start times matter, but
    • only if you’re a boy, and
    • only if you live in a big city
    • only until 8 AM

What they’re saying about Sleep, Baby!

[testimonials]

Why Does My Teen Sleep So Much?

Why does Jackie sleep so much?

As Jackie’s mother was asking the question, I was already suspecting that Jackie actually didn’t sleep enough!

They Sleep So Much, and Yet So Little!

Jackie (not her real name) is a pretty typical high-school sophomore. She’s a good student. She plays three sports. When I met her she was running track in the fall. The problem, Jackie told me, was that she needed to do homework, but she couldn’t keep her eyes open during dinner. She was afraid that her grades were going to suffer if she couldn’t complete her school work.

She would wake up at 6:30 in the morning. Or rather, Jackie’s mother would wake her up at 7. There’s no way Jackie would wake up on her own. On Saturdays and Sundays, the girl would wake up at 10.

The school day would go fine. Jackie didn’t report any sleeping or even drowsiness during the day. Immediately after school she’d go to track practice, four days per week. She’d compete once per week. After track, Jackie would come home, eat dinner and do homework. Most nights Jackie wouldn’t get to bed until after 11 PM.

Lately the fatigue was catching up to Jackie. By dinner time she was wiped out. That’s when they sought my advice.

The Story

sleep so much 2
Do I sleep so much?

I took a complete history from Jackie and her mother. She was healthy (no snoring, no asthma), had no emotional or drug problems (that she would admit to). There was no television in her room. The rule in house was that no cell phones or tablets were allowed in the bedroom. Jackie’s parents kept to this rule as well. She had been a good sleeper up to this point. There was no family history of parasomnia.

The answers to these and other questions led me to believe that the reason for Jackie’s sleepiness after school was not a result of any health or emotional problem. Jackie would sleep so much after school because she wasn’t sleeping enough at night.

Teens Don’t Sleep So Much

Teenagers are supposed to get 9 1/2 hours of sleep every night. But on average, teens get 7- 7 1/2 hours. In addition, the teen sleep cycle is delayed compared to their younger peers. The teenage sleep cycle is such that they will tend to want to fall asleep at 11 PM, but they’ll need to wake up at 8:30 AM in order to get their 9 1/2 hours. Jackie was already in school when her brain wanted her to be waking up!

As a result, Jackie was genuinely exhausted by the time track practice was over. Her mother had wondered if Jackie needed to quit track so that she could get her homework done earlier.

Sports are Good for Kids

I explained that the issue was not track, it was the early wake-up time required by Jackie’s school. Jackie was glad to hear this. She really enjoyed track. She enjoyed the competition, and several of her good friends were on the team.

Need a SLEEP COACH?

In fact, vigorous exercise is good for teens (as it is for all of us!) I suspect that if Jackie wasn’t running track she probably would not be doing as well as she was. Teens who participate in sports tend to be more organized than their non-athletic peers, not least because sports schedules force the young person to be more efficient with study and homework.

The Fix for Jackie

sleep so much 3
If I’m going to sleep so much, I’m going to do it by the lake

Jackie’s situation is far from unique. High school administrators are well aware of sleep issues among the student body. With so many students involved in after-school activities, the sleep-deprivation problem is made worse. To respond to the problem, many schools have devised an ingenious solution: the study hall.

Study hall of course is an old concept. But these days schools are permitting extra study hall periods dedicated to homework.

There are several advantages to the student who is permitted to get homework done during school hours. Not least, student-athletes like Jackie can return from practice, shower, eat dinner, and go to sleep!

The solution is not ideal, however. The best solution would be to start school later for high schoolers. Such solutions in fact have been tried in several school districts, with positive results.

Jackie’s guidance counselor was enormously helpful. With her help, Jackie was able to schedule two extra study hall periods per week, which were enough to allow Jackie to finish all her homework before track practices and meets.

The take-home lesson for parents is that your teen isn’t sleeping as much as you think. In fact, they probably aren’t sleeping enough. I recommend trying to figure out how much sleep your teen is getting at night. Chances are very good that she is not getting 9 1/2 hours. If daytime sleepiness is becoming a problem, then some kind of intervention would help you.

That’s where I come in. I help parents solve their teenagers’ sleep problems. If you are dealing with a sleepy teenager, who nods out during school, or upon returning home, I can help.