Later Start Times Help Teens Obtain Adequate Sleep

Starting high school classes at 8:30 a.m. boosts students’ grades, mood, and driving performance, a new multisite study shows.

The three-year study assessed the impact of later high school start times on about 9,000 students in grades 9 to 12, and 500 in grades 6 to 8, in five public school districts in three states. Kyla Wahlstrom, Ph.D., director of the University of Minnesota’s Center for Applied Research and Educational Improvement, led the study, which was funded by the Centers for Disease Control and Prevention (CDC).

Decades of research show that teenagers need 9 to 9.25 hours of sleep for optimal alertness. Most teenagers find it hard to fall asleep before 11 p.m., Wahlstrom said, because pubertal changes in the biological clock delay the evening onset of melatonin secretion. The start of sleep occurs about an hour later in adolescents than in prepubertal children.

Starting classes at 8:30 a.m. aligns the school day with the adolescent biological clock, Wahlstrom told Psychiatric News. This start time, she said, allows most teenagers to sleep about eight hours and still have time to eat breakfast and get to school.

Eight hours are a practical compromise, she noted, between teenagers’ sleep need, parents’ work hours, and typical school hours. It also allows students to obtain enough rapid eye movement (REM) sleep to process information from the previous day and consolidate memory.

In Wahlstrom’s study, about 60 percent of students in schools that started at 8:35 a.m. slept eight or more hours on school nights. In the latest-starting school, which opened at 8:55 a.m., about 66 percent of students averaged eight or more hours of sleep. In schools starting at 7:30 a.m., only 34 percent of students did so.

Most U.S. public high schools start classes at 8 a.m.; many start before 7:30 a.m. In large metropolitan areas, school bus pickups start before 6 a.m., requiring a wake-up time of 5 a.m. or earlier. Some schools offer extra-credit classes or hold sports practice before the school day starts. Schools and sports organizations, Wahlstrom asserted, need to avoid scheduling early-morning activities that cut into teenagers’ sleep.

Eight hours of sleep represents a tipping point that separates greater or lesser amounts of at-risk behaviors, Wahlstrom’s group and others have found.

The CDC’s most recent Youth Risk Behavior Survey, conducted in 2007, found, for example, that nearly 70 percent of U.S. high school students averaged less than eight hours’ sleep on school nights, and 40 percent averaged six hours or less. Sleep-deprived students reported more symptoms of depression, thoughts of suicide, substance use, and other at-risk behaviors than those who slept eight hours or longer.

Wahlstrom’s group replicated and extended those findings. When schools in their study started later, academic performance improved. After the Jackson Hole, Wyo., high school delayed its start time from 7:35 a.m. to 8:55 a.m., for example, students earned better grades in their first-period core subjects of English, math, science, and social studies. Attendance rose, and tardiness declined.

Car crashes caused by Jackson Hole drivers aged 16 to 18 also fell, from 23 crashes in the year prior to the change to seven afterward, a 70 percent decline. That’s a significant drop, Wahlstrom said, resulting in greater safety of both teens and the general public.

In addition, students who averaged eight hours of sleep or more reported fewer symptoms of depression than those who slept less than eight hours. When asked to describe their mental state in the prior two weeks, she said, the longer the students slept, the less often they reported that they felt sad, unhappy or depressed, hopeless about the future, nervous or tense, or worried.

Teens sleeping eight hours or more also reported lower use of caffeine, alcohol, and illicit substances than their shorter-sleeping peers. A report on the study findings is in preparation.  ■