In describing my research position to other classmates, the first reaction has been that shifting school hours would have no effect on sleep quality and quantity of students; they would accordingly shift their own hours, resulting in no net gain of sleep, while acting as an inconvenience to the rest of society.  My first assertion is that adapting school hours to intrinsic adolescent sleeping patterns would increase the amount of sleep students gain.  The hours at which students fall asleep is dependent upon an internal biological clock that is difficult to change.  By shifting school hours to suit this clock, students would maintain a similar bedtime while increasing the amount of sleep.  

Sleep time is dependent upon environmental factors, on sleep/wake homeostasis, and the circadian system.  Sleep/wake homeostasis describes the balance between how long a person has been awake with how long and how deeply one needs to sleep.  This would partially account for adolescent sleep patterns over the course of the week, where students sleep more on the weekends to account for lack of sleep during the week.  

The circadian sleep pattern, however, describes the sleep shift in adolescents over the course of the day.  Sleepiness is initiated in part by the secretion of melatonin, a hormone.  Studies have shown that melatonin secretion in adolescents is shifted to a later hour than that in adults and children.  Melatonin secretion is dependent upon light exposure, and researchers suggest that adolescents are more sensitive to light, even at night, pushing back the hours of melatonin secretion and resulting in a later bedtime and less deep sleep.  Melatonin has also been shown to be related to pubescence, which would explain why sleeping patterns tend to shift at a similar age.  Sleep/wake homeostasis patterns may also undergo rearrangement during adolescence.  

Schools that changed their starting times have supported the idea that intrinsic clocks play a significant role in determining sleep times.  Even after changing school hours, students in these schools reported a bedtime consistent with that before the change.