Although a class schedule with later start times allows colleges students to get more sleep, it also gives them more time to stay out drinking at night. As a result, their grades are more likely to suffer, suggests a research abstract that will be presented Tuesday, June 14, in Minneapolis, Minn., at SLEEP 2011, the 25th Anniversary Meeting of the Associated Professional Sleep Societies LLC (APSS). Results show that later class start times were associated with a delayed sleep schedule, which led to poorer sleep, more daytime sleepiness, and a lower grade-point average. Students with later class start times also consumed more alcohol and reported more binge drinking. Students who were "night owls¹" with a natural preference to stay up later were more likely than "morning types" to have a delayed sleep schedule and to consume more alcohol.

"Later class start times predicted more drinking, more sleep time and modestly lower grades, overall," said co-lead author Pamela Thacher, PhD, associate professor in the Department of Psychology² at St. Lawrence University in Canton, N.Y. "Later class start times seemed to change the choices students make: They sleep longer, and they drink more."

Thacher speculated that drinking more alcohol, which is known to disrupt sleep, may reduce the benefits of getting more sleep.

"The effects of later class start times might include more sleep," she said. "But this might be offset³（抵消，弥补） by lower quality sleep, which in turn might affect their ability to engage, intellectually, with their coursework."

Thacher, co-author Serge Onyper, PhD, and their research team studied 253 college students. Participants completed cognitive⁴ tasks and a one-week retrospective（回顾的，怀旧的） sleep diary, as well as questionnaires about sleep, class schedules, substance use and mood. All data were collected on a weekday one month before the end of the semester. GPA was recorded from university records and self-reports.

Results also show that students were attempting to catch up on sleep on the weekends with later rise times and longer sleep durations. Average total sleep time for weekdays and weekends was 8.0 hours.

The authors noted⁵ that the results are much different from previous studies of school start times in middle and high school. Those studies show numerous benefits of later school start times, which tend to decrease truancy⁶（旷课，逃学） , improve mood and indirectly⁷ promote learning.

In a study published in 2008 in Behavioral Sleep Medicine, Thacher found that 60 percent of student participants at a liberal-arts college reported engaging in a single night of total sleep deprivation⁸ once or more since starting college. Statistical⁹ analyses found that pulling an "all-nighter" was associated with lower grades.