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Dr. Kyla Wahlstrom: School start time

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With research showing that teens are biologically predisposed to need morning sleep, California and Florida have recently passed laws requiring later start times for middle and high schools—and nationwide, school districts, and individual schools, are making similar adjustments.

On Thursday, August 24, 2023, SciLine interviewed: Dr. Kyla Wahlstrom, a senior research fellow and lecturer in University of Minnesota’s College of Education and Human Development. She discussed topics including: the biological reasons that teenagers have a hard time feeling fully awake before 8 a.m.; what research shows are the ideal start times for elementary schools, middle schools, and high schools; the benefits of later school start times for teens’ physical and mental health, safety, and academic performance; and how many hours of sleep teenagers need, and how their parents can help them get it.

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KYLA WAHLSTROM: Hi, I’m Dr. Kyla Wahlstrom, a faculty member at the University of Minnesota in the College of Education and Human Development. I study educational policies that affect the learning of students and the leadership that is needed to effect policies and enact them in schools across the United States.


Interview with SciLine

What are the biological reasons that teenagers have a hard time feeling fully awake before 8:00 a.m.?


KYLA WAHLSTROM: Teenagers have, during their adolescent period, a shift in their brain that is called a circadian phase delay shift or just a sleep delay shift that is biologically determined. And it’s true for—universally true for all teenagers as they go through their adolescence. And so, the biological reasons for this shift have to do with how the body matures until it reaches about age 19. And then it will shift back to what the person was pre teenage and in into and through adulthood. So, we all have genetically predetermined sleep-wake cycles and preferences. But during the teenage years, all teenagers have this shift in their brain that causes them to not feel sleepy until about 10:45 or 11 at night, and they don’t really fully awake—the brain doesn’t wake up—until about eight in the morning.

What does research show are the ideal start times for elementary, middle, and high schools?


KYLA WAHLSTROM: Teens are unable to really wake up and be fully functioning before 8:30 in the morning. And in fact, we do know that 20-25% of all teenagers, if their school starts early, will be sleeping at their desks in their first hour of class. So, the ideal start time for high schools is 8:30, middle schools 8:00. And then when we look at elementary students, elementary students have a very flexible sleep schedule. It’s quite different than that of an adolescent. And so, with an elementary age student and their flexibility, schools can start actually earlier than often they do and they can start before the high schools at eight or 8:30 to accommodate busing schedules and so on. Elementary students just need between nine and eleven hours of sleep every night. And it just depends on when the parents put them to bed. If they get their full amount of sleep, they’re able to get up and be starting school at 7:45, 8:00.

How many hours of sleep do teenagers need?


KYLA WAHLSTROM: Teenagers optimally should be getting nine hours and fifteen minutes every night. Every night—that includes weekends. The lowest amount, the tipping point amount is eight hours per night. And anything less than eight hours is into the danger zone. And it significantly causes negative outcomes when you have less than eight hours per night. It’s interesting, I think sometimes both parents and teens think that they can just catch up on their sleep on the weekend. That is a total false assumption. Because it’s sort of like if sleep is food for the brain, which I believe it is, it’s like OK, we’re going to deprive ourselves of adequate food three days out of the week, but then we’re going to gorge on food on the weekend. That’s not healthy. And neither is getting less than eight hours of sleep average every night. Because that’s what keeps the body fueled and the brain operating at optimum capacity—when the child, the student, gets eight hours minimum of sleep every night.

How can school start times affect teens’ physical and mental health, safety, and academic performance?


KYLA WAHLSTROM: Any teen that’s getting less than eight hours of sleep per night is at risk for the following kinds of negative outcomes that we have documented as to be true for a student getting less than eight hours. For instance, we do know that there is greater use of drugs, cigarettes, alcohol, when a teen is getting less than eight hours. We also know that there is a significant link between teenage depression any sleep amount that is less than eight hours. So depression—we have depression, physical health, mental health. And then of course the safety issues have to do with their driving ability. They’re inexperienced drivers, when you have a sixteen year old behind the wheel of a car—and their decision making and their reflexes are severely affected by a lack of sleep. So, the teenagers that are sleep deprived are much more statistically significantly likely to be in a car crash, to make poor decisions, to even run into us on the road. So, it’s a pretty serious outcome when you don’t have enough sleep in your teenage child.

The other thing has to do with academics, and the academics are related to what we know through cognitive science and memory building. And during the nighttime hours, all of the information that a student would be learning during the day is cataloged by the brain into various file folders, I would call it, just as a way to organize the information. And so, when a child or a student has adequate sleep, the amount of things that are remembered for academic reasons are greatly enhanced, and the students then do better academically. On the other hand, when you have a sleep-deprived student, they often don’t have the amount of sleep that would allow them to fully categorize all of their memories and their learning. And as a consequence, it affects their grades. So, we know statistically that academic performance is enhanced and in fact achieved at best levels when the student gets eight or more hours of sleep every night.

How do later school start times affect teens’ relationships with their parents and families?


KYLA WAHLSTROM: We have surveyed parents—and in all of our surveys, more than 92% of the parents responded to say that their teenager was easier to live with after the later starting time. Many parents have anecdotally told me that their child is a different child. They are able to speak with them at breakfast, they are chatty in the car, they don’t have moody episodes and fly off the handle. The parents are just saying it’s remarkable that this has made such a change in their child’s life, and their family dynamics, as a result of having adequate sleep. So, the outcome with the families is also equally important.

How can parents help teens get enough sleep even if their school day starts early?


KYLA WAHLSTROM: Parents play an important role in their child—their teenager’s sleep cycle and their ability to fall asleep. A couple of things that are really important, and one has to do with the parent’s control—if you want to use that word—control over the child’s cell phone use. Cell phones in the bedroom have been incredibly detrimental to teen sleep. When they’re doing social media during the night, if they use the phone for an alarm, those kinds of things are going to cause the brain to wake up, and the child will be unable to fall back asleep. So, the parent and the family is best off if they just take the cell phones—everybody’s cell phones goes into the kitchen to a charging station, and it spends the night there. And then the child can wake up without having being interrupted during their sleep time. The other thing that’s really important is parents need to be educated themselves about their teenagers’ sleep patterns, sleep cycle. When you think about it, parents of an infant—they know a lot about what’s going on with their child’s development and their child’s sleep-wake cycles. And they talk to their pediatrician about how that all develops over time. But often parents of teenagers don’t know about the sleep-wake cycle of teenagers, and how that is universally a developmental stage that these teenagers can’t fall asleep much before eleven, and they don’t wake up until about eight in the morning.

Whose input needs to be considered when a community is considering changes to school start times?


KYLA WAHLSTROM: The important factors that arise in terms of making this decision or living with this decision is having community discussions and input about it. It’s really important that everybody who has a stake in this—a stakeholder—in the school schedule of when the children—elementary, middle school, high school—go to school, it needs to be a community decision.

Do you have any advice for reporters covering proposed changes to school start times?

[Posted August 24, 2023 | Download video]