Whether or not you know any high school students that actually get nine hours of sleep each night, that's what U.S. federal guidelines currently prescribe. A new Brigham Young University study found that 16-18 year olds perform better academically when they shave about two hours off that recommendation.

"We're not talking about sleep deprivation," says study author Eric Eide. "The data simply says that seven hours is optimal at that age."

The new study by Eide and fellow BYU economics professor Mark Showalter is the first in a series of studies where they examine sleep and its impact on our health and education. Surprisingly, the current federal guidelines are based on studies where teens were simply told to keep sleeping until they felt satisfied.

"If you used that same approach for a guideline on how much people should eat, you would put them in a well-stocked pantry（餐具室，食品室） and just watch how much they ate until they felt satisfied," Showalter said. "Somehow that doesn't seem right."

In the new study, the BYU researchers tried to connect sleep to a measure of performance or productivity. Analyzing data from a representative sample of 1,724 primary and secondary school students across the country, they found a strong relationship between the amount of sleep youths got and how they fared on standardized tests.