“It’s too expensive to start the school day later.”

“Extracurriculars will suffer if we start school later.”

“We shouldn’t coddle teens by pushing school start times.”

These are just some of the arguments against later school start times for teens. Although the public has become increasingly aware of the sleep deprivation epidemic among teens in the US, the cost and logistic difficulties associated with addressing the problem have stymied attempts at reform. But what has been framed as a policy issue for education, is, at its deepest root, an issue of biology.

Teens need an average of 8 to 10 hours of sleep each night.[1] But only 20% of adolescents in the US report getting adequate sleep on school nights.[2] Insufficient sleep in teens has been linked to increased risk of unintentional injury and death, poor school performance, obesity, negative mood and increased irritability, and increased substance abuse.[1] Research also indicates that even short term sleep deprivation can alter neural plasticity,[3] the process by which the brain reorganizes in response to experience. Neural plasticity is important for learning and memory development during adolescence.[4]

So why don’t teenagers put down their X-box controllers, homework, or phones at 9 pm and get the rest they need? Perhaps it is just not that simple. Not only is the ability to make future-oriented decisions,[5] like going to bed earlier to avoid being sleepy the next day, still developing throughout adolescence, but biology is running the show when it comes to sleep.

The ability to fall asleep is influenced by two major biological processes: (1) the body’s circadian rhythm or internal clock, which drives the 24-hour sleep-wake cycle; and (2) homeostatic sleep drive, which is the body’s internal timer that generates a pressure for sleep when too much time has elapsed since the person last slept.

Both of these processes interact with the brain and are sensitive to hormonal changes that occur during puberty. Melatonin secretion, one of the major chemical agents that tells your brain when to get sleepy and go to bed, is low during periods of wakefulness, peaks at maximum sleepiness, stays relatively high during sleep, and declines again near one’s wake-time. Melatonin also acts on the flip side, promoting sleep onset by increasing homeostatic sleep drive.

So how does this relate to teenagers? Research shows that melatonin levels rise about two hours later in the day for adolescents than most children and adults, indicating a “sleep phase delay”. This physically makes it more difficult for teens to get to bed earlier.[6]

Because sleep phase delay pushes adolescent bed times later, and school start times force early wake times, most adolescents suffer from insufficient sleep during the week. On weekends, adolescents attempt to make up for this deficit by waking later.[2]The chart below shows that between 9th and 12th grade, there is a 1.2 to 1.5 hour difference between the amount of time teens are sleeping during the week and the amount of sleep they get on the weekends.

While this may seem like a logical solution, this sleep discrepancy between weekday and weekend sleep actually exacerbates the problem. Inconsistent sleep can be just as damaging as insufficient sleep,[7] and catch-up sleep further delays sleep pressure and circadian signals for sleep.[8] Because of the expectations we place on teenagers in terms of acceptable waking hours, their strategies to cope with sleep deprivation may be making their problems even worse.

In 2014, the American Academy of Pediatrics recommended that secondary schools start no earlier than 8:30am to account for these biological changes in teen sleep cycles.[9] So why do 5 out of 6 middle and high schools in the US still start before 8:30? Opponents of later school start times say that changing school schedules affects everyone – teachers, bus drivers, and especially parents. Even in the face of the evidence for delayed start times, many parents, educators, and policy makers have argued that starting school early will help adolescents to learn adult responsibility. After all, the “real world” doesn’t start work at 11:00AM, does it? If this argument is indeed about teaching adolescents responsibility and to make good decisions, the biology is again, not in alignment with adult beliefs.

The brain regions and networks responsible for an adolescent’s ability to make future-oriented decisions,[10] such as the prefrontal cortex (PFC), are still developing throughout adolescence. Pair an immature PFC with the biology of a tired teen, and what you get is nothing that resembles a good decision-maker.  Expecting teens to operate on an adult’s schedule does nothing to teach them responsibility, but actually makes responsible decision making even more difficult.[11]

Another argument that has been proposed is that even if schools started later, it wouldn’t matter because teens would just stay up later playing X-box, or scrolling through Instagram. However, a three-year longitudinal study, conducted with over 9,000 students in eight public high schools in three states, revealed high school start times at 8:30am or later allow for more than 60% of students to get at least eight hours of sleep per night, suggesting teens were not staying up later in response to the later wake times. After implementing later school start times, teens in these schools reported lower depressive symptoms relative to peers in other schools, lower use of caffeine, showed improved academic performance on standardized state and national achievement tests, higher grades in math, English, science, and social studies classes, and improved attendance. In two districts, the rate of car crashes for high school age drivers dropped by 65-70%.[12] Given car accidents are a leading cause of death for teens,[13] these findings alone would justify efforts to improve adolescent sleep.

Lack of sleep among adolescents is a major public health issue, one with an immense cost to society. National poll results indicate more than half of teens drive drowsy and 15% of drivers in 10th-12th grade drive drowsy at least once a week.[2] The National Highway Traffic Safety Administration conservatively estimates drowsy driving crashes result in 1,550 deaths, 71,000 injuries, and $12.5 billion in monetary losses per year.[14] Other consequences are more difficult to monetarily quantify but are no less critical. A 2014 study found that each hour of lost sleep for teens was associated with a 42% increase in considering suicide and a 58% increase in suicide attempts.[15] Insufficient sleep is associated with increased risk of cigarette, marijuana, and alcohol use in adolescence,[16] with one study finding a 6% increase for every 10 minutes later that a teen goes to bed.[17] Inadequate sleep has broad implications for health and well-being, cognitive functioning, and academic performance.[18] Given the overwhelming consequences, policy makers, educators, and parents should make a shift to prioritize adolescent sleep, and, in doing so, will prioritize the well-being of adolescents themselves.

[1] National Sleep Foundation. (2000). Adolescent Sleep Needs and Patterns. Retrieved from: https://sleepfoundation.org/sites/default/files/sleep_and_teens_report1.pdf

[2] National Sleep Foundation. (2006). Sleep in America Poll. Retrieved from: https://sleepfoundation.org/sites/default/files/2006_summary_of_findings.pdf

[3] Beebe, D. W., Rose, D., & Amin, R. (2010). Attention, learning, and arousal of experimentally sleep-restricted adolescents in a simulated classroom. Journal of Adolescent Health, 47, 523-525.

Tononi, G., & Cirelli, C. (2014). Sleep and the price of plasticity: From synaptic and cellular homeostasis to memory consolidation and integration. Neuron, 81, 12-34.

[4] Kanwal, J. S., Jung, Y. J., & Zhang, M. (2015). Brain plasticity during adolescence: Effects of stress, sleep, sex, and sounds on decision making. Anatomy & Physiology, 6, e135.

[6] Taylor, D. J., Jenni, O. G., Acebo, C., & Carskadon, M. A. (2005). Sleep tendency during extended wakefulness: Insights into adolescent sleep regulation and behavior. Journal of Sleep Research, 14(3), 239-244.

[7] Barber, L. K., Munz, D. C., Bagsby, P. G., & Powell, E. D. (2010). Sleep consistency and sufficiency: Are both necessary for less psychological strain? Stress and Health, 26, 186-193.

Fuligni, A. J., & Hardway, C. (2006). Daily variation in adolescents’ sleep, activities, and psychological well-being. Journal of Research on Adolescence, 16(3), 353-378.

[8] Crowley, S. J., & Carskadon, M. A. (2010). Modifications to weekend recovery sleep delay circadian phase in older adolescents. Chronobiology International, 27(7), 1469-1492.

[9] American Academy of Pediatrics. (2014, August). Let them sleep: AAP recommends delaying start times of middle and high schools to combat teen sleep deprivation. Retrieved from: https://www.aap.org/en-us/about-the-aap/aap-press-room/Pages/Let-Them-Sleep-AAP-Recommends-Delaying-Start-Times-of-Middle-and-High-Schools-to-Combat-Teen-Sleep-Deprivation.aspx

[10] van den Bos, W., Rodriguez, C. A., Schweitzer, J. B., & McClure, S. M. (2015). Adolescent impatience decreases with increased frontostriatal connectivity. Proceedings of the National Academy of Sciences, 112, E3765-E3774.

[11] Durmer, J. S., & Dinges, D. F. (2005). Neurocognitive consequences of sleep deprivation. Seminars in Neurology, 25, 117-129.

[12] Wahlstrom, K., Dretzke, B., Gordon, M., Peterson, K., Edwards, K., & Gdula, J. (2014). Examining the impact of later high school start times on the health and academic performance of high school students: A multi-site study. Center for Applied Research and Educational Improvement. St. Paul, MN: University of Minnesota.

[13] Centers for Disease Control & Prevention. (2010, May). Mortality among teenagers aged 12-19 years: United States, 1999-2006. National Center for Health Statistics Data Brief No. 37.

[14] National Highway Traffic Safety Administration. (2002). National Survey of Distracted and Drowsy Driving Attitudes and Behaviors. Retrieved from: http://www.nhtsa.gov/people/injury/drowsy_driving1/survey-distractive03/index.htm

[15] Winsler, A., Deutsch, A., Vorona, R. D., Payne, P. A., & Szklo-Coxe, M. (2015). Sleepless in Fairfax: The difference one more hour of sleep can make for teen hopelessness, suicidal ideation, and substance use. Journal of Youth & Adolescence, 44, 362-378.

[16] McKnight-Eily, L. R., Eaton, D. K., Lowry, R., Croft, J. B. Presley-Cantrell, L., & Perry, G. S. (2011). Relationships between hours of sleep and health-risk behaviors in US adolescent students. Preventative Medicine, 53(4-5), 271-273.

[17] Troxel, W. M., Ewing, B., & D’Amico, E. J. (2015). Examining racial/ethnic disparities in the association between adolescent sleep and alcohol or marijuana use. Sleep Health, 1(2), 104-108.

[18] Carskadon, M. A. (2011). Sleep’s effect on cognition and learning in adolescence. Progress in Brain Research, 190, 137-143.