Starting the school day before 8:30 in the morning is bad for kids. It’s bad for their physical health, their mental health and their academic performance.

So says the American Academy of Pediatrics, which issued a formal policy statement Monday recommending that middle and high schools do away with those 7:30 or 8:00 a.m. school bells and begin no later than 8:30.

“Chronic sleep loss in children and adolescents is one of the most common – and easily fixable – public health issues in the U.S. today,” said pediatrician Judith Owens, lead author of the policy statement. She added:

The research is clear that adolescents who get enough sleep have a reduced risk of being overweight or suffering depression, are less likely to be involved in automobile accidents, and have better grades, higher standardized test scores and an overall better quality of life. Studies have shown that delaying early school start times is one key factor that can help adolescents get the sleep they need to grow and learn.

The group said that about 40 percent of high schools in the U.S. start before 8, while only 15 percent start at 8:30 or later. The median start time is 8 a.m. for high schools, the policy statement said, while more than 20 percent of middle schools start at 7:45 or later.

It cited a National Sleep Foundation poll that “found 59 percent of 6th through 8th graders and 87 percent of high school students in the U.S. were getting less than the recommended 8.5 to 9.5 hours of sleep on school nights.”

Of course, if students went to sleep earlier, it wouldn’t matter. But they don’t. What keeps them up?

Home work, said the group, and extracurricular activities, after-school jobs and staying up late enmeshed in technology.