If you went to high school in the US, you may recall early morning extracurriculars, sleeping through first period algebra, or bleary-eyed late-night study sessions (as opposed to other wide-awake “study sessions” we told our parents we were having).

As it turns out, early school start times for US high schools are built on a shaky scientific foundation, as journalist and parent Lisa Lewis lays out in her new book, The Sleep-Deprived Teen.

She details why high schools in the US tend to start early, the science behind why that’s bad for kids, and how later school start times can benefit not only teenagers, but, well… everyone.

Our early start times are a bit of a historical accident.

In the first half of the 20th century, schools tended to be small and local—most students could walk.

To minimize costs associated with busing, Lewis describes how many districts staggered school start times so they could use the same buses for transporting elementary, middle, and high school students.

Yet Lewis reports that by 2019, a mere 22 percent of high school students reported regularly getting at least eight hours of shut-eye, according to the CDC.

Yet here we are, decades later, with average school start times in 2017 beginning at 8 am and 40 percent of schools starting even earlier.

This is a dramatic change from a century ago when high schools in the eestern US began at 9 am, notes Lewis.

Lewis describes one study, published in 2018, in which students slept an additional 34 minutes each school night when their Seattle district shifted start time to 8:45 am That might not seem like much, but many students and families provided positive feedback, as did the teachers, with one describing the morning ambiance as “upbeat”—an adjective many of us might find unfathomable for first period.