Why does school start so early? Blame 1970s planning.

When Ameen Al-Dalli was a sophomore in high school in 2014, each weekday before sunrise he would walk the quiet, tree-lined streets of Fairfax, Virginia, to the school bus stop. Because Ameen's public school, about five miles away, started at 7:20 a.m., the bus came early. "I feel drowsy and just like, ugh, I want to go home," he told National Geographic filmmakers during his walk in the gloom.

This wasn't always the case for high schoolers. A few generations ago, the bell rang around 9 a.m. for most American kids. But according to the Centers for Disease Control and Prevention, at least 75 percent of schools surveyed in more than 40 states for a 2015 report started before 8:30 a.m., with a significant number starting in the 7 a.m. hour.

What happened? A lot of things, including suburbanization, the energy crisis, and a big cultural shift around child safety norms. But the early start times for American schools have largely been imposed by transportation needs: Getting kids to school became a lot more complicated in the age of sprawl.

In the 1960s and 70s, when developers began to build housing on the peripheries of urban centers, they often neglected to consider the importance of locating schools centrally. Instead, schools were often built on even more peripheral (and inexpensive) land, and a lack of pedestrian infrastructure made walking to them difficult and dangerous. Cultural changes also kicked in: This was around the time that parents began to grow more fearful that a stranger would harm their child en route to school, and hoofing it to class became less prevalent. In 1969, for instance, almost half of children five to 14 usually walked or biked to school; by 2009, that percentage had dropped to 13 percent. These shifts in the built environment and cultural norms created a need for more busing.

The streets of this Des Moines suburb aren't always conducive to walking to school. (Charlie Neibergall/AP)

But when the energy crisis hit in 1973, suburban schools had to cut transportation costs. Separate fleets of buses generally accommodated different ages so that elementary, junior high, and high school students all arrived at school at the same time. Their solution: A two- or three-tiered system that staggered school start times, so that the same fleet of buses could serve the entire student population. High-school students usually got picked up and dropped off earliest—no one wanted first-graders huddling in the pre-dawn darkness—then middle schoolers, and finally elementary school kids—with the result that high schools and middle schools opened earlier. Urban public schools often followed suit, even if they didn't have the same busing needs, so that children and parents in the same region all followed the same schedule.

"This was great from a cost perspective," says Terra Ziporyn Snider, co-founder and director of the nonprofit advocacy group Start School Later, which has been active in a growing national movement to, well, start school later. "During these same years, sleep research began to show adolescents' need for more sleep, and at later hours than adults. However, the schedules had already been changed, and municipalities were reluctant to switch again."

That research, which recently led both the CDC and the American Academy of Pediatrics to urge later start times at American schools, shows that teenagers need at least nine hours of sleep a night, and that during puberty the body starts producing the sleep-inducing hormone melatonin at 11 p.m.—a full two hours after adult bodies do. And teens keep pumping the stuff out until around 8 a.m.; perhaps not surprisingly, virtually all American teenagers don't get nine hours of nightly rest.

The impact of that chronic sleep deprivation is not limited to their AP Calc scores: Studies indicate that this contributes to higher rates of car accidents, criminal activity, alcohol use, and mood disorders.

Ziporyn Snider notes that those most vulnerable to early start times are economically disadvantaged children. "These kids don't have enough compensating mechanisms," she says. "If you oversleep and miss the bus, for example, your parents are less likely to have a car. So you're not going to school." And across the board, kids' physical and mental health suffer when they are sleep-deprived. "A huge number of students are using stimulants," she says. "They have eating disorders, depression, anxiety."

The start-time issue has inspired fierce debates among parents in school districts nationwide. While municipalities are often reluctant to disrupt schedules and delay their schools' start times, some have done so at the urging of parents or advocacy organizations like Start School Later. (Ameen Al-Dalli's school, for instance, changed its start time to 8:00 a.m. during his junior year.) "We've found that once communities approach this issue as a non-negotiable health imperative, they move forward," says Ziporyn Snider.

Not all parents agree: In Montgomery County, Maryland, which pushed its bells back in 2015, many have objected to the longer days for the young elementary school students, some of whom now don't begin class until 9:25. Others note declining participation among older kids in after-school sports or activities. Recent research, however, has shown academic benefits: Schools that delayed their starting times to 8:30 a.m. or later during the past two decades are enjoying improved attendance and graduation rates.

And a 2011 paper from the Brookings Institution's Hamilton Project argued that the overall economic benefits of delaying school start times by one hour for middle and upper grades delivered an extra $17,500 in lifetime earnings per student because of better academic performance.

But delaying bells can also drive up costs: That same Brookings paper computed a cost of up to $1,950 per student for that extra hour of sleep. And the logistics involved in delivering far-flung suburban students to schools on time can be fiendishly complex: In suburban Howard County, Maryland, for example, a pair of University of Maryland researchers developed a computer algorithm to optimize the staggered start times of elementary, middle, and high school students in the county public school system. For maximum efficiency, the researchers found that high school needed to begin at 7:25. (The district is now weighing a series of possible start-time changes.)

A more long-term cost- and energy-efficient solution might involve ditching the buses and making suburban community schools more walkable, with more traffic lights and crosswalks so that kids can travel safely to school on foot. (This inner-ring Cleveland suburb, for instance, has got walking to school down—it doesn't even use buses—though not all places have the benefit of its density.)

Top-down efforts are also having some success. Over the past three years, Maryland and New Jersey have passed bills that either mandate research on school start times or incentivize schools to start later. Last month, the California State Senator Anthony Portantino introduced a bill that would require the state's junior high and high schools to start no earlier than 8:30 a.m. And the California Congresswoman Zoe Lofgren has put forward federal bills that push for later school start times. Her latest requests a study examining the relationship between start times and adolescent health, well-being, and performance.  

"People are sensing that change is coming," says Ziporyn Snider, who's confident that American kids, in city and suburb alike, will soon be getting a at least a little more sleep. "Though it will likely vary from state to state and place to place, later school start times are going to become more the norm again."