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Key points
- A meta-analysis of studies of high school and middle school school start times shows that later start times afford some benefits for students.
- Students with later start times slept longer, were less sleepy, and had fewer instances of negative mood.
- There were no benefits found for sleep quality, academic performance, or positive emotional mood.
- Insufficient number of studies did not allow conclusions about comparisons by gender, race/ethnicity, or socioeconomic status.
A study for which I was a co-author was recently published in the journal Pediatrics describing a meta-analysis review of the growing literature on school start times (Yip et al., 2022).
A meta-analysis is a rigorous statistical method for comparing results of all the available studies on a topic. The authors identified 28 studies that met their inclusion criteria and the total number of students was 1.75 million high school and middle school students. In ten of the studies, investigators were able to make assessments after a school district had changed from earlier to later start times.
Results showed some benefits of later start times—including longer sleep duration, lower levels of sleepiness, and lower levels of negative mood. While those relations were significant, the effect sizes were relatively small.
Many variables, however, showed no relation to school start time, including sleep quality, chronotype, and academic performance. For other outcomes of interest, positive emotional well-being, academic performance, and other developmental domains—behavioral, physical, and cognitive—there were too few studies to analyze.
Likewise, because too few studies were available, comparisons by gender, race/ethnicity, or socioeconomic status were not possible. Some comparisons were made between public and private schools, and students in private schools with later start times tended to have better sleep quality and later wake times.
What This Tells Us About School Start Times
On the positive side, it is heartening that some benefits of later start times were discovered. Advocates of starting school later will welcome these results.
On the other hand, definitive conclusions are not yet possible for many important questions. Besides the lack of sufficient numbers of studies, there are some methodological concerns of the vast majority of studies, including those in this review. While some studies used objective measures of sleep, most relied on student self-report.
And as the authors point out in the Limitations section, there has been no study controlling for the Hawthorne Effect—a phenomenon suggesting that positive outcomes are often reported any time a novel change purported to deliver a benefit is introduced. When people are expecting outcomes to be better, in other words, they tend to report that the change worked in the expected direction. In the sleep domain, more studies with objective measures would likely diminish such an effect.
A more fundamental problem in start-time research is that it is impossible to conduct randomized controlled trials (RCT) studies where the students, teachers, and researchers are blind to which schools are in the experimental or control group. RCTs are designed to control for biases, including expectancy effects.
As more studies are done to address limitations discovered in this review, school policymakers will have more information on which to base their decisions about whether and how to adjust school start times.
References
Yip, T., Wang, Y., Xie, M., Ip, P. S., Fowle, J., & Buckhalt, J. (2022). School start times, sleep, and youth outcomes: a meta-analysis. Pediatrics, 149(6).
