The early start to classes causes teenagers to
lose much needed sleep that puts them at risk of
becoming moody and performing poorly in school,
A survey of students aged 12 to 15 years old found
they lost an average of two hours of sleep on the
nights before a school day, affecting their work
and alertness in class.
More than one-third of high schools rang the bell
to begin classes at 7:30 a.m. or earlier, a separate
2003 survey found, and 85 percent of high schools
begin the day before 8:15 a.m., the report said.
Students living long distances from school face
even earlier wake-up calls to catch rides.
Sleepiness is associated with moodiness and poor
school performance, and a chronic shortage of sleep
correlates with a greater propensity to take up
smoking or to be involved in car crashes, the researchers
At the time adolescents enter high school their
bodies are undergoing changes to their biological
clocks -- called circadian rhythms -- that govern
when they become sleepy and fully awake. The changes
tend to make them go to bed later and wake up later,
said the report published in the journal Pediatrics.
In the study, 60 teens kept sleep diaries during
a month in summer when schools were closed and again
during a few months of the school year.
While they lost sleep on school nights, they slept
30 minutes longer than usual on weekend nights during
the school year and on summer nights, indicating
they were not just using weekends to catch up on
sleep during the school year.
"Weekend sleep and weekend wake times may represent
a return to an intrinsic circadian rhythm that is
lost during the week because of the imposed school
schedules," said the study by researchers at Northwestern
University and Evanston Township High School in
The findings point to sleepy students in the mornings
who tend to become more alert in the afternoons.
Teachers attested to this in an accompanying report
published in the journal and written by pediatric