By 6:45, Lizzy staggers onto the school bus, where she joins dozens of other sleepy teen-agers on their way to Horace Greeley High School in Chappaqua, which begins at 7:45. 
Sleep researchers are discovering that adolescent sleepiness in the morning has a physiological basis. And educators are beginning to take notice of the research and questioning whether the school schedule -- originally based on an agrarian economy when students were needed home in the afternoon to do farm chores -- is optimal for teaching today's teen-agers. 

http://www.nytimes.com/1997/11/23/nyregion/scientist-says-sleepy-teen-agers-aren-t-just-tired.html?pagewanted=all&src=pm