Teens tend to be in their deepest sleep around dawn, when they typically need to get up for school, researchers say. (CBC)

Giving teens 30 extra minutes to start their school day leads to more alertness in class, better moods, less tardiness, and even healthier breakfasts, a small study found.

"The results were stunning. There's no other word to use," said Patricia Moss, academic dean at the Rhode Island boarding school where the study was done. "We didn't think we'd get that much bang for the buck."

The research appears in July's Archives of Pediatrics & Adolescent Medicine. The results mirror those at a few other schools that have delayed starting times by 30 minutes or more.

Researchers say there's a reason why even half an hour can make a big difference. Teens tend to be in their deepest sleep around dawn — when they typically need to get up for school. Interrupting that sleep can leave them groggy, especially since they also tend to have trouble falling asleep before 11 p.m.

"There's biological science to this that I think provides compelling evidence as to why this makes sense," said Brown University sleep researcher Dr. Judith Owens, the study's lead author and a pediatrician at Hasbro Children's Hospital in Providence, R.I.

An Archives editorial said the study adds to "a growing body of evidence that changing the start time for high schools is good for adolescents."

The fact that the study was in the exclusive setting of St. George's School in Middletown, R.I., doesn't necessarily weaken the results. Owens acknowledged that there might be more hurdles to overcome at poorer, public schools, including busing schedules, parents' work hours and daycare for younger siblings.

'It's about adult convenience'

While these issues have killed many proposals, some public high schools have adopted later starting times.

Mel Riddile, associate director at the National Association of Secondary School Principals, favours later class times for teens but said most districts oppose it. "It's about adult convenience, it's not about learning," he said. "With budget cuts, it's going to make it more difficult to get this done."

Many parents and teachers at St. George's were opposed but reluctantly agreed to the study after a presentation by Owens, whose daughter was a junior there.

Overall, 201 high school students completed sleep habit surveys before and after the nine-week experiment last year. The results were so impressive that the school made the change permanent, Moss said.

Starting times were shifted from 8 a.m. to 8:30. All class times were cut by five to 10 minutes to avoid a longer school day that would interfere with after-school activities. Moss said improvements in student alertness made up for the lost instruction time.

The portion of students reporting at least eight hours of sleep on school nights jumped from about 16 per cent to almost 55 per cent. Reports of daytime sleepiness dropped from 49 per cent to 20 per cent.

First-period tardiness fell by almost half. Students reported feeling less depressed or irritated during the day, health centre rest visits dropped substantially, and the number of hot breakfasts served more than doubled. Moss said the healthier breakfasts probably aided alertness in class.

The study was designed to look at changes in sleep habits and behaviour and didn't examine academic performance. It also lacked a control group of students who didn't experience a change in start times, another limitation.