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A Minnesota study of 18,000 students whose schools switched to a later start time found kids slept more but posted only slightly higher grades. Credit: Thom Lang/Getty Images

The physical and mental health benefits of getting a good night’s sleep are indisputable. What’s less clear is whether starting school later in the morning will prompt kids to sleep more and consequently learn more during the school day. Fewer studies have looked at academic achievement after a later morning bell. Some have found improved student performance. Some haven’t. 

A new study in Minnesota documents what happened to 18,000 students in grades 5 through 11 after four school districts postponed the start of the school day by 20 to 65 minutes. Student grades increased a little, raising students’ grade point averages by an extra 0.1 points, on average. That’s the equivalent of moving from, say, a B average of a 3.1 to a B average of a 3.2.  

Despite concerns that kids would just stay up later at night if school started later in the morning, many students reported sleeping more. After the switch in start times, students were 16 percent more likely to meet the recommended hours of sleep, which is nine or more hours for students in grades 5 and 8 and at least eight hours for students in grades 9 and 11.

Researchers from the University of Minnesota and the Bloomington, Minnesota, public schools characterized the academic benefits as “small” but the sleep increases as “large.” 

The study was instigated by the school district of Bloomington, home to the Mall of America and headquarters of International Dairy Queen, because it had been considering whether to shift its schools to a later start time and wanted more data to inform the decision. Local officials pressed the snooze button on this sleep debate during the Covid pandemic. But the researchers presented their study, “Changes in school start time have a significant effect in the amount of sleep and reported grade point average of students,” in April 2021 at a session of the annual meeting of the American Educational Research Association. 

I thought the research was interesting in a national context as it slightly bolsters the evidence for starting school later but isn’t quite the knockout punch that advocates hoped to make.

Nationally, Minnesota has been at the forefront of starting school later in the morning. Edina, an affluent Minneapolis suburb, is believed to be the first town in the U.S. to shift to a later start, moving in 1996 from 7:20 a.m. to 8:30 a.m. in response to medical research about teen sleep. In 2014, the American Pediatric Association recommended an 8:30 a.m. start time for high schools and middle schools so that teens can get sufficient sleep.  

Schools have been slow to heed the doctors’ advice. Only 17 percent of U.S. high schools start the day at 8:30 a.m. or later, according to the most recent federal data. The average start time for high school across the nation remains a half hour earlier, at 8:00 a.m.. South Carolina has the latest high school start time in the nation of 8:34 a.m., followed by Alaska, Minnesota and Iowa. The earliest is Louisiana, where high schools start at 7:30 a.m., on average.

Advocates often assert that later start times have been proven to improve academic performance but I was surprised to learn how murky the research evidence is. Researchers don’t always find academic gains and where they exist, they tend to be small.  For example, a 2015 study of elementary school students in Wayzata, Minnesota, found only small increases in reading and math scores and the increase wasn’t seen for all students.  A 2018 study reported increases in grades and attendance in one Seattle high school but not in another. 

“The findings from all of the research regarding the relationship between start time, sleep duration, and academic performance are not totally conclusive,” said Kyla Wahlstrom, a national expert of school start time research at the University of Minnesota who was not involved in the current study, via email. 

“That said, after 25 years of my looking at academic performance and start time, there is no question in my mind that greater sleep, meaning eight hours or more per night for teens, does in fact yield better academic performance,” Wahlstrom said. “This is because there is incontrovertible evidence that sleep enhances cognition and memory.” 

In the current study, four Minnesota districts — Wayzata, Burnsville, Richfield, and Mounds View — moved to a later school start time between 2016 and 2019. One shifted from 7:25 a.m. to 8:35 a.m.; a second shifted from 7:30 a.m. to 8:20 a.m.; a third shifted from 7:33 a.m. to 8:00 a.m., and a fourth shifted from 8:10 a.m. to 8:30 a.m.. Researchers compared results for 18,000 students in these districts with 20,000 students in similar districts that continued to start the day early. Districts were matched by similar demographic characteristics, such as race and ethnicity, language and family income. Researchers also factored in how students responded to survey questions about how much they cared about doing well in school.

One surprising result were the positive outcomes for 5th graders, who not only slept more but also achieved higher grades when they started school later. Advocates for later start times often focus on teens and are less worried about younger kids’ sleep. Perhaps the assumption that it’s more natural for younger kids to go to sleep earlier and wake up earlier needs to be re-evaluated. By contrast, the researchers didn’t see extra academic benefits for 11th graders after switching to a later schedule, compared to similar students in districts that continued to start the day early. 

There seems to be no harm to children in switching to later school schedules but there are many obstacles. Julio Caesar, a research scientist at Bloomington Public Schools and one of the study’s authors, explained that teachers unions are often resistant to moving teachers’ work schedules. Many communities have a limited number of buses and have to stagger school start times, forcing younger kids to start earlier when older kids start later. Those changes can upset family schedules and create resistance from parents. Starting school later leads to ending school later and that can cut into precious after-school sports time. 

One silver lining to the Covid pandemic is that there are fewer logistical challenges to later start times when you’re learning remotely from home and school activities are canceled. My daughter’s middle school in Brooklyn switched to a 9 a.m. start during the current 2020-21 school year and I’ve noticed that she’s less groggy in the morning. It will be interesting to see what her school and others decide to do about the schedule next year when normal life returns. 

Advocates for later start times see an opening now with so many school norms upended. That’s something to dream about.

This story about school start times was written by Jill Barshay and produced by The Hechinger Report, a nonprofit, independent news organization focused on inequality and innovation in education. Sign up for the Hechinger newsletter.

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Jill Barshay writes the weekly “Proof Points” column about education research and data, covering a range of topics from early childhood to higher education. She taught algebra to ninth-graders for...

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  1. Thank you for your thoughtful commentary! Unfortunately, any changes to the education system appear to take place on the geologic time scale. The organization, Start School Later has been active on this topic since 2011. Their home page clearly states their objective. “Restoring traditional school start times, as recommended by the American Academy of Pediatrics, American Medical Association, and the Centers for Disease Control, is a practical and necessary solution with broad and immediate benefits for children of all ages.” ​Is anyone heeding the advice of physicians? I’ve included a link to one of my blogs.
    https://handleeducation.com/synchronize-with-teens-chronobiology/

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