During puberty, teenagers' daily circadian rhythms are altered and their natural bedtime is shifted to about 11 p.m., according to scientists. This finding, paired with studies that show that teens require at least 8 1/2 hours of sleep per night, suggests that students should not rise until at least 7:30 a.m. This is usually when the first period begins in many American high schools so classrooms are often filled with students too dragged out to learn effectively.
Now, a study from the University of Minnesota has shown that the sleep deficit incurred by tired high-schoolers can lead to memory loss, decreased alertness and creativity, and increased depression. After the Minneapolis Public School District changed its high school start time from 7:15 a.m. to 8:40 a.m., researchers found students were more likely to stay awake in class and be more focused while doing their work (see here). The same has been noted in Ohio, where Dayton's Belmont High School has a start time of 9 a.m. With the teen-friendly start, school counselor Lynne Slaven said students who have more sleep arrive in the morning alert and with better attitudes.
According to the Cleveland Plain Dealer, many schools are reluctant to make such changes to their schedules because it conflicts with the work schedules of parents and guardians. Also, later start times mean students wouldn't get home until the late afternoon or early evening, posing a conflict for after-school jobs and extracurricular activities. Ultimately The Gadfly, from personal experience, figures that students will be better off if they get more sleep in their beds instead of at their desks.