The sun is hot. Water is wet. Teenagers like to sleep in.

These truths we know to be self-evident.

The American Academy of Pediatrics embraced the latter in a report this week, saying classes for middle and high school students should start no earlier than 8:30 a.m.

The report cites research showing that teens who don't get enough sleep suffer physical and mental health problems – specifically, they tend to have an increased risk of becoming obese and/or depressed.

A lack of sleep can also increase the chances of getting into a car crash and letting academic performance slip.

Getting to bed early isn't necessarily the answer. The pediatricians say teens' natural sleep cycles make it difficult for them to hit the sack before 11 p.m.

Educators, though, say pushing start times back isn't as easy as it sounds.

"There's a cost-benefit analysis you've got to make there, and even though the research is there, there's too many other factors that overcome that," said Quakertown School District Superintendent William Harner.

The school board there has decided to zig despite decades of research telling them to zag. The district will start high school an hour earlier this year with the first bell at 7 a.m.

Why? In part, the logistics of student busing.

Starting high school earlier will mean younger kids in the district will be able to start later. It's too dangerous, Quakertown officials say, to have 11-year-olds waiting for the bus outside at 6:15 a.m. in the the dark winter.

Starting earlier also means that high school technical-education students will get 50 minutes more instruction; finishing earlier means academics will be less frequently interrupted by afternoon sports and extracurriculars.

"My athletes in the afternoon are going to get a full school day in. My Upper Bucks Technical School students are going to get a full school day in," said Harner. "Isn't that more important than a fraction of a grade that's predicted of better success if they had another hour of sleep?"

The Philadelphia School District high schools have start times varying from 7:30 to 8:30. Without committing to a change, Superintendent William Hite says moving times back would be easier for them because their high school kids already rely on public transportation.

The district's three new high schools – The LINC, Building 21 and The U School – will commence classes at 9:00 a.m.