. Author manuscript; available in PMC: 2012 Jun 1.

Published in final edited form as: Pediatr Clin North Am. 2011 Apr 1;58(3):649–665. doi: 10.1016/j.pcl.2011.03.002

Table 1.

Quasi-Experimental Studies Involving Differences in School Start Times

Authors	Grade Level	Analytic Design	Comparison	Findings
Dexter et al.⁵¹	10th-11th grades	Between-Groups	Two nearby schools serving students with similar demographics, one starting at 7:50 am, the other at 8:35 am.	Students at the school that started at 7:50 reported significantly less sleep and a trend towards more sleepiness. Sleepiness ratings at both approached the pathologically sleepy range.
Wolfson et al.⁵²	7th-8th grades	Between-Groups	Two nearby schools serving students with similar demographics, one starting at 7:15 am, the other at 8:37 am.	Students at the school that started at 7:15 reported significantly less sleep on school nights and greater sleepiness, and had more school-documented tardiness. Reported class grades differed across schools for 8th graders, but not 7th graders.
Hansen et al.⁵⁶	Incoming 9th grade honors students	Within-Group	Student sleep diaries the month before school started were compared to those completed the first two weeks of high school and again several months later.	Weeknight sleep duration dropped dramatically from summer into the school year. It then lengthened a bit across the school year, but remained well below summertime levels.
Carskadon et al.⁵⁷	Students Shifting 9th to 10th grades	Within-Subjects	Students wore actigraphs in the spring of 9th grade at a school that started at 8:25 am, and again in the fall of 10th after transitioning to a school that started at 7:20 am. Sleepiness was also assessed during each time period.	School night bedtimes did not change over time, but rise time became significantly earlier with the transition to the 7:20 am start time, resulting in less sleep. Students’ physiological sleepiness was higher during the second time point as well.
Wahlstrom⁵³-⁵⁴	9th-12th grades	Mixed Within-Group and Between-Groups	7 schools in one district (District A) changed start time from 7:15 am to 8:40 am. Letter grades and enrollment data were compared before and after the schedule change. Also, after the school start time change, student-reported sleep and affect ratings were compared against analogous ratings in a nearby, demographically-similar district that had a 7:30 am start time (District B).	After start time change, students in District A changed schools less, and those who changed schools had higher attendance rates. There were no differences in overall student grades from before to after the start time change, but methodological issues complicated analyses. Focusing on the post-change time period, compared to District B, students in District A had only slightly later bedtimes, but markedly later rise times, resulting in almost an hour more sleep per night. Also students in District A reported less daytime sleepiness, less tardiness due to oversleeping, and marginally fewer sick days and symptoms of depression.
Danner & Phillips⁵⁵	9th-12th grades	Mixed Within-Group and Between-Groups	Students reported on sleep before and after start times were shifted from 7:30 am to 8:30 am in a county-wide district. Motor vehicle crash data for 17-18 year-olds in the county were contrasted with trends for other counties in the state.	Compared to before the change in start times, after the start time had been changed students’ school night sleep time increased significantly, weekend night sleep time decreased significantly, and there was a reduction in motor vehicle crashes by teens in the county. During the same time period, teen crashes were stable or increased slightly elsewhere in the same state.