Hitting the snooze button: hundreds of high schools across the country are starting classes later so you can sleep in.

• Author: Hoffman, Jann
• Position: NATIONAL

More American teens are catching up on their z's--not just on weekends, but on school days too.

The nearly 20-year effort to start high school classes later in the morning--pushed in some cases by students--has gained momentum, with hundreds of schools in dozens of districts across the U.S. bowing to mounting research on the adolescent body clock.

In the past two years, high schools in Long Beach, California; Stillwater, Oklahoma; Decatur, Georgia; and Glens Falls, New York, have pushed back their opening bells, joining schools in Connecticut, North Carolina, Kentucky, and Minnesota. The Seattle school board is considering the issue. The superintendent of Montgomery County, Maryland, supports the shift; and the school board in Fairfax County, Virginia, is working to develop options for starts after 8 a.m. Last summer, Secretary of Education Arne Duncan posted his endorsement for later start times on Twitter.

New research suggests that later high school starts have widespread benefits. Sleep experts at the University of Minnesota studied eight high schools before and after they moved to later start times. They found that the later a school's start time, the better off students were on measures like mental health, car crash rates, attendance, and, in some schools, grades and standardized test scores.

Researchers have known for some time that quality sleep directly affects learning. During R.E.M. (rapid eye movement) sleep--a period of deep sleep that happens three to five times a night in well-rested people--the brain is wildly active, sorting and categorizing the day's data. The more sleep you get, the better the information is absorbed.

"Without enough sleep," says Jessica Payne, an assistant professor of psychology at the University of Notre Dame in Indiana, "teenagers are losing the ability not only to solidify information but to transform and restructure it, extracting inferences and insights into problems."

The solution is not as simple as hitting the sack earlier. During puberty, as hormones surge and the brain develops, teenagers have a later release of the "sleep" hormone melatonin, which means they may not feel drowsy until about 11 p.m. Nighttime use of technology like smartphones and iPads, which emit a blue light that tricks the brain into thinking it's still daytime, further slows the release of melatonin.

Twitter Activism

One of the schools that recently got on board with later start times is Rock Bridge High School in...