Most teenagers in the United States start the school day too early each morning, robbing them of the sleep they need to concentrate properly and remain healthy, according to a study.
Fewer than one in five middle and high schools in the United States start at 8:30 am or later, as recommended, according to data from the Centers for Disease Control and Prevention (CDC).
Research from the American Academy of Pediatrics (AAP) has found that adolescents are biologically programmed to stay asleep longer than adults.
Depriving teens of that sleep could wreak havoc on their academic performance, the CDC said in its Morbidity and Mortality Weekly Report.
"Getting enough sleep is important for students' health, safety, and academic performance," said Anne Wheaton, lead author and epidemiologist in CDC's Division of Population Health.
"Early school start times, however, are preventing many adolescents from getting the sleep they need."
In 2014, the AAP urged secondary schools not to begin classes until 8:30 am to give teens the 8.5 to 9.5 hours of nightly sleep they need.
But only 17.7 percent of US high schools actually start at the recommended hour.
The effects are not limited to academic performance, and researchers warned students may also suffer outside the classroom.
"Insufficient sleep is common among high school students and is associated with several health risks such as being overweight, drinking alcohol, smoking tobacco and using drugs," the CDC study found.
Many parents have urged schools to delay start times, but administrators often refused, arguing that after-school extra-curricular activities would be too hard to organize.
An estimated two out of three US students are sleep-deprived, according to a 2013 CDC study.