By: Mercedes White

Do your teenagers complain that the school day starts too early? They aren’t alone. A 2007 study of 280 teenagers in Philadelphia found that most students believed their school’s 7:30 a.m. start time is too early, according to Science Daily. Moreover, 90 percent of students said they believed their performance would improve if school started later.

A growing body of research substantiates these claims. Delaying school start times by one hour, from roughly 7:30 to 8:30, increases standardized test scores by at least 2 percentile points in math and 1 percentile point in reading, according to a North Carolina study by economist Finley Edwards described in Education Next. Students get more sleep and have fewer absences. Another benefit of late start is that with less unsupervised time after school, kids spend more time on homework and watch less TV.

Starting early has the most effect on older middle schoolers, supporting the theory that hormonal changes make it hard for adolescents to get to sleep in the early evening, Edwards writes. During adolescence, a teen’s biological sleep patterns shift toward later times for both sleeping and waking, according to the National Sleep Foundation. This means it is quite natural for teens not to be able to fall asleep until 11 p.m. at the earliest. Their research scientists have found that teens need 9.25 hours of sleep to function best.

Start times have no effect on elementary students performance, according to Edwards study. Districts could swap elementary and secondary school start times to improve achievement without spending more on busing, Edwards suggests.