Many adolescents actually have a common sleep disorder called a delayed sleep phase syndrome. The disorder, which is caused by changes in the body's internal clock associated with puberty, means it is normal to be a "night owl" at just about the time your family wants to go to sleep. It also means you want to sleep later in the morning. This pattern is hard to change, so teens end up sleep-deprived because school starts early, before the required nine to nine-and-a-half hours of sleep have occurred.