What time should the school day begin? School start times vary considerably, both across the nation and within individual communities, with some schools beginning earlier than 7:30 a.m. and others after 9:00 a.m. Districts often stagger the start times of different schools in order to reduce transportation costs by using fewer buses. But if beginning the school day early in the morning has a negative impact on academic performance, staggering start times may not be worth the cost savings.
Proponents of later start times, who have received considerable media attention in recent years, argue that many students who have to wake up early for school do not get enough sleep and that beginning the school day at a later time would boost their achievement. A number of school districts have responded by delaying the start of their school day, and a 2005 congressional resolution introduced by Rep. Zoe Lofgren (D-CA) recommended that secondary schools nationwide start at 9:00 or later. Despite this attention, there is little rigorous evidence directly linking school start times and academic performance.
In this study, I use data from Wake County, North Carolina, to examine how start times affect the performance of middle school students on standardized tests. I find that delaying school start times by one hour, from roughly 7:30 to 8:30, increases standardized test scores by at least 2 percentile points in math and 1 percentile point in reading. The effect is largest for students with below-average test scores, suggesting that later start times would narrow gaps in student achievement.
The primary rationale given for start times affecting academic performance is biological. Numerous studies, including those published by Elizabeth Baroni and her colleagues in 2004 and by Fred Danner and Barbara Phillips in 2008, have found that earlier start times may result in fewer hours of sleep, as students may not fully compensate for earlier rising times with earlier bedtimes. Activities such as sports and work, along with family and social schedules, may make it difficult for students to adjust the time they go to bed. In addition, the onset of puberty brings two factors that can make this adjustment particularly difficult for adolescents: an increase in the amount of sleep needed and a change in the natural timing of the sleep cycle. Hormonal changes, in particular, the secretion of melatonin, shift the natural circadian rhythm of adolescents, making it increasingly difficult for them to fall asleep early in the evening. Lack of sleep, in turn, can interfere with learning. A 1996 survey of research studies found substantial evidence that less sleep is associated with a decrease in cognitive performance, both in laboratory settings and through self-reported sleep habits. Researchers have likewise reported a negative correlation between self-reported hours of sleep and school grades among both middle- and high-school students.
I find evidence consistent with this explanation: among middle school students, the impact of start times is greater for older students (who are more likely to have entered adolescence). However, I also find evidence of other potential mechanisms; later start times are associated with reduced television viewing, increased time spent on homework, and fewer absences. Regardless of the precise mechanism at work, my results from Wake County suggest that later start times have the potential to be a more cost-effective method of increasing student achievement than other common educational interventions such as reducing class size.