Students typically are sleep deprived due to a combination of poor sleep quality, a late bedtime, and an early start to the day.

Article:  Sleep habits and factors associated with short sleep duration among Japanese high-school students: A community study

Type of source: primary

Summary: The research was conducted using  a survey administered to one class in each grade at 34 different high schools across Japan.  After collecting data, the researchers still were unsure if a short sleep time results in bad academic performance, but they did figure out that sleep deprivation is caused by lack of a restful sleep and late bedtimes not an early wake-up time.

Link: http://onlinelibrary.wiley.com/doi/10.1111/j.1479-8425.2003.00079.x/full