People were tested to see how this principle works. The subjects were woken up every 15 minutes, or one phase of sleep was taken away. The following day, they reported the usual emotional and physical symptoms of sleep loss (Dahl, R).
Most scientists and researchers say that there are 4 phases of sleep. Some would call wakefulness stage zero. In stage one, the person is somewhat conscious. In tests, when subjects were told to indicate faint tones that were played during this phase, they successfully indicated about half of the tones. Phase 2 is described as being the first phase of actual sleep. When the same test was done on subjects in phase 2, no response was given. Phase 3 and phase 4 are the deepest phases of sleep. Phase 3 is moderate, and phase 4 is extremely deep sleep. These are the hardest to wake someone up from and they only occupy about 20% of our sleep time. They are the phases that must be reached to achieve sufficient sleep (Coren 30-31).
According to most studies, adolescents require between 8.5 and 9.25 hours of sufficient sleep every night (Stein, M). Dr. Mary Carskadon and Dr. William Dement found that adolescents starting at twelve years old require at least 10 hours of sleep a night (Coren 120). A small 15% of teenage students get at least 8.5 hours of sleep on weekdays, and over 25% of teenage students get less than 7 hours of sleep on weekdays ("Sleepy Teen Troubles"). .
Ninety-nine female high school students in Sao Paolo, Brazil were part of an experiment to see how much sleep students were getting. The students were mostly fourteen through sixteen years old, and they attended a public school from 7:15am to 5:05pm Monday through Friday. The questionnaire that they were given asked about things like their health status, complaints that they had about their sleep, and their sleep habits. The test showed that students slept two hours less on schooldays than weekends, and woke up 3.