With the onset of puberty, adolescents begin to experience a sleep-phase
delay in their biological clock (i.e., circadian rhythms) and develop a natural tendency to fall asleep later in the evening
and wake up later in the morning. Even
adolescents who are sleep deprived tend
to feel alert in the evening, making it
more difficult for them to go to bed at a
reasonable hour. Sleep is triggered by the
release of melatonin, a natural body hormone. Toward dawn, melatonin shuts
off as the hormone cortisol increases, signaling the individual to wake up. The
pattern and timing of melatonin secretion makes it hard for adolescents to fall
asleep and wake up at the times necessary to get enough restful sleep. Schools
with start times before 8:30 a.m. place
students at a disadvantage in terms of
arousal and alertness, not only for early
morning classes but also throughout the
day because adolescents’ biological
rhythms are out of sync with typical
school routines.