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The Latest Sleep Research: Delayed School Start Times and the Impact on Children and Teens

By: SleepScore Labs  |  April 23rd, 2021

Chronic sleep deprivation is a critical threat to the mental and physical development, academic potential, and safety of children worldwide. Increasing the number of children who get sufficient sleep was recently included as a core objective for Healthy People 2030. Delaying school start times (no earlier than 8:30 AM) has been identified as an essential modifiable public policy that can improve childhood learning, development, and health and wellness. This change in policy is also supported by teens’ biological tendency toward being night owls.

By requiring students to go to sleep early and wake up early for school, we are placing them in a perpetual “social jet lag”’ – teens’ internal clocks do not match up with their social time. Teens will often fall asleep late (1 AM) and wake up early (6 AM), thereby restricting their total sleep time and worsening their sleep deprivation. Since teens require at least 8-9 hours of sleep a night, there are cascading mental and physical consequences to this social jet lag. With less than 20% of schools starting at 8:30 AM or later, recent research looked at the feasibility and effectiveness of delaying school start times to improve sleep in adolescents and children. Another study also examined whether short and inconsistent sleep impaired school readiness in preschool children.

Study 1:

In order to evaluate the impact of changing school start times on sleep for elementary, middle, and high-school students, Dr. Lisa Meltzer and colleagues surveyed around 28,000 students and their parents. Middle schools in the Cherry Creek School District in Colorado delayed their start times by 40-60 minutes (to 8:50 AM), high schools delayed theirs by 70 minutes (to 8:20 AM), while elementary schools started 60 min earlier (to start at 8:00 AM). According to the lead study author, the elementary school students began school an hour earlier over the course of the study so that older students could be picked up later.

Students and their parents were surveyed once before the time change, 1 year after the time change, and 2 years after the time change. The annual survey measured sleep-wake and sleep quality variables ranging from bedtime, wake time, sleep duration, sleep quality, and daytime sleepiness.

The elementary students who began school an hour earlier had no changes in their sleep duration and had similar sleep quality before and after the school time change. Fascinatingly, middle school students went to bed about 10 minutes later but slept an additional 37 minutes, leading to an average of 30 minutes of extra sleep. Similarly, high school students went to bed 15 minutes later and slept for an extra hour, leading to an extra 45 minutes of sleep. Importantly, all significant results were maintained after 2-years and the benefits of later start times were similar across sociodemographic and free/reduced lunch groups.

This is the first large-scale, long-term, and representative study to concurrently examine the impact of changing school start times for students across K-12. Although the findings overwhelmingly support the benefits of later start times, there are three important study limitations to consider. First, all results were based on self-reported surveys – objective sleep measures, which are known to be far more reliable, were not used. Next, only one survey per year (in the spring) was administered. It is possible that sleep patterns can vastly change during the year. Finally, and most importantly, this paper only examined sleep outcomes. It remains unclear whether the sleep gained by delaying school start times had a quantifiable effect on academic outcomes (grades/GPA), cognitive outcomes (attention/learning), psychological well-being (stress), and physical/developmental outcomes (brain plasticity).

Study 2:

Dr. Dylan Jackson from Johns Hopkins University examined whether sleep duration and bedtime consistency among preschool children would be associated with school readiness. School readiness, according to authors, was conceptualized as children entering school ready to learn. This is underpinned by several specific domains: early learning skills, self-regulation, social-emotional development, and physical health & motor development. The authors included a sample of over 15,000 pre-school-aged students (3-5 years old). Caregivers completed the National Survey of Children’s Health three times between 2016-2018. The survey assessed several components of children’s lives ranging from health, well-being, and development to sleep duration and sleep consistency.

The authors found that short sleep duration (<7 hours) was associated with poorer school readiness across all domains when compared to those sleeping 10 hours or more. Importantly, children sleeping 8 hours or more had no increased risk in reductions to early learning skills, self-regulation, social-emotional development, or physical health & motor development. These findings support guidelines from The American Academy of Pediatrics: pre-school-aged children should obtain between 10 to 13 hours of sleep per day. In addition to sleep duration, should sleep bedtimes be consistent daily and on the weekends? The authors found that children with inconsistent bedtimes also exhibited significant reductions in school readiness – but to a slightly lesser extent.

This study found that children with short or inconsistent sleep are vulnerable to reductions in school readiness which may impede early learning skills. Notwithstanding the study’s contributions, the study did not use objective sleep measures which would give a more complete picture of preschooler’s sleep – especially since parent reports may not be entirely accurate. It is also important to note that this work is correlational; it remains unclear if poor sleep explicitly causes reductions in school readiness. Future work is still needed to determine whether the negative consequences of insufficient and inconsistent sleep translate to other age groups, namely elementary, middle and high-school students.

Increasing Sleep In Children for Academic Achievement and Development

Sleep is critically important for the health, neurological development, and academic success of children. Established guidelines recommend that teens get between 8-10 hours of sleep per night. Pre-school-aged children likely need even more – between 10-13 hours of sleep per night. Recent research suggests that delaying school start times by up to an hour can significantly improve sleep duration in teens. Inversely, excessively short sleep duration (<7 hours) and inconsistent bedtimes are associated with impaired school readiness in preschoolers. Together, this work highlights the need for radical reform to school policies. We can help support the developmental and educational needs of adolescents worldwide by ensuring that children obtain their recommended amount of quality sleep.

Article 1:

Jackson, D. B., Testa, A., & Semenza, D. C. (2021). Sleep Duration, Bedtime Consistency, and School Readiness: Findings from the 2016 to 2018 National Survey of Children’s Health. Journal of Developmental & Behavioral Pediatrics.


Article 2:

Meltzer, L. J., Wahlstrom, K. L., Plog, A. E., & Strand, M. J. (2021). Changing school start times: impact on sleep in primary and secondary school students. Sleep.

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