Teenagers today often do not get enough sleep, something their developing bodies and brains require. Early school start times are thought to be part of the reason. After a Colorado school district moved its high school start time from 7:10 a.m. to 8:20 a.m., it found that students reported getting an average of 48 minutes more sleep a night and they said they felt less sleepy and generally more engaged in academics. The district also adjusted the middle school start time — from 8 a.m. to 8:50 a.m. — and researchers found that middle-schoolers began logging an average of 31 minutes more sleep each night. The researchers surveyed more than 15,000 Cherry Creek School District high school and middle school students a year after the start times were changed and found that fewer students reported feeling too sleepy to do their homework (down from 46 percent to 35 percent among middle-schoolers and down from 71 percent to 56 percent among high school students), while scores on a measure of academic engagement improved.

Seattle schools had similar results on sleep times after changing their start times, and also reported improved attendance and better grades, according to research published late last year.

Besides the potential positives for academics, longer and better-quality sleep for teens also has been found to contribute to lower blood pressure, better cholesterol levels and less likelihood of being overweight, researchers reported last year in the journal Pediatrics. Experts generally agree that teens should get eight to 10 hours of sleep each night. To help achieve that, at least three medical groups — the American Medical Association, American Academy of Pediatrics and American Academy of Sleep Medicine — recommend that middle and high schools start no earlier than 8:30 a.m.

— Linda Searing