- Puberty has been beginning earlier; in many cases, it can start in elementary school.
- With puberty comes later sleep timing.
- School start times should be in sync with children in all grades.
Puberty is not a discrete developmental event; rather it is a process typically beginning between 8 and 13 years in girls and 9 and 14 years in boys. The age at which children begin puberty has been decreasing for decades. One review and meta-analysis of studies from studies done in countries across six continents concluded that from 1977 to 2013, the age of pubertal onset decreased by around three months per decade. A factor that has been associated with earlier puberty is increased rates of child obesity. Obesity in children has been linked to later diseases including Type 2 diabetes and cardiovascular problems. Also of concern is that independent of body size, early puberty increases the risk of cancers. For example, girls who reach puberty earlier have been found in longitudinal studies to be at greater risk for breast cancer in adulthood.
Evidence has accumulated over decades that the process of puberty affects sleep/wake timing. The consensus among pediatric sleep researchers is that with puberty, the timing of sleep shifts later such that if freed from school or work demands for waking up early, children go to sleep later and wake up later than they did before puberty began.
The term "social jetlag" has been used to describe a mismatch between ideal sleep timing and the timing of school attendance. While it is indisputable that the use of social media and other environmental factors affect social jetlag, there is also compelling evidence that biological changes drive the changes in sleep patterns.
This evidence has driven some sleep scientists and clinicians to join nonprofessional advocates in a movement to convince school districts to start school later for older students. The benefits are assumed to be that sleep duration will increase, better academic performance will be achieved, and emotional/social behavior problems will decrease.
The movement has been successful by any standard. Many school districts have moved start times later; the California legislature mandated later start times, and several other states are considering doing the same. In the majority of cases, because of bus schedules, starting high schools (and sometimes middle schools) later means that elementary schools will start earlier.
Considerable evidence has been found for changes to later sleep timing for children who begin puberty early. For example, one study found that 8-year-old girls experiencing early puberty slept about an hour later than girls of the same age for whom puberty had not begun. The emphasis on later start times for older students is based on the fact that more older children in later grades have begun and are in some stage of puberty. While that emphasis is appropriately directed, it must be recognized that many children in elementary school have begun puberty, and starting their classes earlier may shift the burden of sleep insufficiency and its risks to health and achievement to them. Achievement in later grades is built upon the foundations laid down in earlier grades, so if poor sleep compromises learning and social/emotional behavior then, it may carry over to poorer outcomes in later grades.
Cheng, T. S., Ong, K. K., & Biro, F. M. (2022). Adverse effects of early puberty timing in girls and potential solutions. Journal of Pediatric and Adolescent Gynecology, 35. 532-535.
Cheng, T. S., Ong, K. K., & Biro, F. M. (2022). Trends towards earlier puberty timing in girls and its likely mechanisms. Journal of Pediatric and Adolescent Gynecology, 35, 527-531.
Eckert-Lind, C., Busch, A. S., Petersen, J. H., Biro, F. M., Butler, G., Bräuner, E. V., & Juul, A. (2020). Worldwide secular trends in age at pubertal onset assessed by breast development among girls: a s
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