In 1997, the Minneapolis School Board made a bold move: it pushed high school start times from 7:15 a.m. to 8:40 a.m. and asked researcher Kyla Wahlstrom to study the ripple effects. What followed wasn’t just a local experiment—it was the beginning of a national reckoning with how early school schedules collide with adolescent biology.
Wahlstrom’s longitudinal study, conducted through the University of Minnesota’s Center for Applied Research and Educational Improvement, tracked outcomes 3 years prior to the change and 3 years after, from 1995 to 2000. The results were quietly revolutionary. Students didn’t use the extra morning time to play videogames or socialize—they slept. And that sleep translated into measurable gains: improved attendance, fewer disciplinary referrals, reduced depression, and even faster homework completion thanks to greater alertness.
This wasn’t just a feel-good story. It was the first robust evidence that shifting the school bell could improve adolescent health and performance.
Sleep, Safety, and Substance Misuse: The Broader Evidence
Since Wahlstrom’s study, the evidence has only grown linking later middle and high school start times to:
More and better-timed sleep
Lower rates of teen motor-vehicle crashes
Reduced symptoms of depression and anxiety
Less use of caffeine, alcohol, and other substances
Improved attendance, graduation rates, and—sometimes—academic performance
Importantly, the academic benefits aren’t evenly distributed. Students from lower-income families and vulnerable racial and ethnic minorities often see the greatest gains. Economists have even flagged later start times as a cost-effective lever for narrowing disparities.
Not a Panacea, But a Prerequisite
Of course, no intervention is a silver bullet. Take Glens Falls, NY: after delaying start times by 45 minutes in 2012, students initially reported 20 extra minutes of sleep. But by spring, bedtime had crept later, erasing the gains in sleep, although students still had fewer tardies and disciplinary issues.
Critics, however, have rightly pointed out the limitations of this study—including self-reported and unvalidated sleep data, homogenous and self-selected samples, and lack of implementation details. And transition years are messy. When a study by the California School Boards Association (CSBA) voiced concerns about logistics, funding, and flexibility involved in a statewide school start time law, for example, they were evaluating responses after just one year of implementation. Their report also leaned heavily on anecdotal feedback and overlooked key details like actual start times adopted or how changes were implemented.
Another recent study suggesting that underprivileged 11- and 12-year-olds might not benefit from later start times sparked sweeping claims questioning the benefit of later start times for anyone, overlooking the study’s narrow scope and contradicting broader research. A more accurate takeaway: even with reasonable start times, sociocultural factors can still disrupt sleep. That’s not exactly groundbreaking. Nor does it say anything about the need to have start times that give all students an opportunity for healthy sleep regardless of whether other factors keep students from using that opportunity.
The Danger of Cherry-Picked Evidence
The conversation often goes astray when critics citing isolated studies as proof that later start times “don’t work” ignore the overwhelming body of research showing otherwise. This kind of selective citation isn’t just misleading—it actively undermines evidence-informed policymaking.
Policymakers deserve a full picture, not a fragmented one. And when the broader literature consistently shows that later start times improve sleep, safety, mental health, and equity—and, even more, that too-early start times actively harm these things— it’s irresponsible to let a single study, especially one with methodological limitations, carry disproportionate weight.
Later Isn’t Enough—But Earlier Is Harmful
Here’s the crux: later start times don’t guarantee healthy sleep. But earlier start times almost guarantee unhealthy sleep, with highly concerning consequences for students, families, and communities. That’s the consensus among sleep researchers, and it’s supported across disciplines—from pediatrics to public health to education policy.
The most successful districts don’t just delay the bell. They educate students and families about sleep, adjust homework and event schedules, and remove structural barriers like long commutes, midnight homework deadlines, late-night practices, and before-school events. Similarly, communities that want to improve sleep health across entire populations have to start by ensuring sleep-friendly school hours but also address the many sociocultural and environmental factors that can disrupt sleep.
What to Remember
Focusing on start times doesn’t mean ignoring other contributors to adolescent sleep loss. But it does mean recognizing that school schedules are one of the few levers we can pull at scale—and the only one proven to work. They’re modifiable. They’re measurable. And they matter.
As we often say:
Starting school later doesn’t guarantee healthy sleep.
But not starting school later guarantees unhealthy sleep.
That’s a tradeoff we can no longer afford to ignore.