CHARLOTTE, N.C. -- As the school year kicks off, school systems across the country are debating early morning bell schedules for high schools.
Increasingly, there's a movement to delay the start time for high schools as evidence shows teenagers benefit from sleeping later.
Research suggest hormones can cause teens to stay up late and sleep late.
"Teenagers have a delayed sleep phase. So, they like to stay up late and they like to wake up late," said Dr. Doug Kirsch, head of sleep medicine at Carolinas Healthcare System.
From Seattle to Chicago to Boston, high schools have been implementing later start times. In some cases, schools report tardiness rate dropped by 35-percent and the number of Ds and Fs fell by half.
Kirsch suggests 8:30 a.m. as an ideal start time for high school students.
"They perform better athletically, they perform better on tests, and they'll make better decisions in the long run," Kirsch said.
It's a matter of safety, too. A recent study suggested North Carolina high schools with later start times reported fewer car crashes involving teens.
But some districts are resistant to the schedule change, citing potential impact on athletic activities, after school jobs, and the bottom line; changing the bus schedules can come with a financial cost.
Currently, Charlotte-Mecklenburg high schools have some the earliest bell times in the district, starting at 7:15 a.m. A CMS spokesman says the district is not considering changing its high school start times.
As featured by WCNC, August 22nd 2016