. Author manuscript; available in PMC: 2017 May 1.

Published in final edited form as: J Sch Health. 2016 May;86(5):363–381. doi: 10.1111/josh.12388

Table.

Descriptions of School Start Time (SST) Studies in Preadolescents, Adolescents, and College-Age Students

Study
Author(s)(Year) Year(s) of Study	Study Design	Sample Size	Age	Location	School Start Times	Outcomes	Key Findings
Carskadon et al. (1998)⁶² Not specified	Longitudinal (before vs after SST change)	26 (same students)	Grades 9–10	Rhode Island	Year 1–9th grade: 8:25 Year 2–10th grade: 7:20	Sleep schedules (sleep diaries and data from electronic wrist monitors), multiple sleep latency tests, polysomnography.	Earlier SST associated with earlier rise time (p < .05), shorter sleep duration (p < .05), shorter REM latency (p < .05), shorter sleep latency on multiple sleep latency tests (p = .004), and more students with REM sleep during multiple sleep latency tests (p NR).
Epstein et al. (1998)⁷² Not specified	Cross-sectional (students in 18 schools)	572	Grade 5	18 schools throughout Israel	Early risers: 7:10 (2+ times/week) Regular risers: 8:00	Sleep duration, bedtime, rise time (weekdays and weekends), sleepiness, daytime functioning, sleep difficulties.	Early risers reported shorter weekday sleep duration (p = .0004), more complaints of feeling tired throughout the day (p = .045), more daytime sleepiness (p = .004), and more difficulty concentrating and paying attention (p = .0001).
Wahlstrom et al. (1998)⁶⁰ Not specified	Cross-sectional (3 districts)	NR	Grades 10–12	Minnesota	District A (Minneapolis): 8:30 District B: 7:25 District C: 7:15	School Sleep Habits Survey³⁵ (study, work, sleep, and school habits, and preferences).	Later SST corresponded to later rise time (p < .0001), same bedtime, and longer weeknight sleep duration (p < .0001). Later SST also associated with less daytime sleepiness (p < .0001), less struggling to stay awake during academic tasks (p < .01 for A vs C), fewer tardies (p < .001), less falling asleep in morning classes (p <.005), fewer depressive symptoms (p < .001 for A vs C), less time spent at work during school week (p < .05), and higher self-reported grades (p < .05).
Wahlstrom et al. (1998)⁶⁰ Not specified	Cross-sectional (3 districts)	NR	Grades 7–8	Minnesota	District A (Minneapolis): 7:35 District B: 8:00 District C: 8:00	School Sleep Habits Survey³⁵ (study, work, sleep, and school habits, and preferences).	Similar associations as in HS students. Later SST corresponded to longer sleep duration (p < .05 for A vs C), same bedtime, and later rise time (p < .05 for A vs C). Later SST also associated with less daytime sleepiness (p < .05 for A vs B), less struggling to stay awake during academic tasks (p < .05 for A vs B), lower depression scores (p < .05 for A vs B), and less hours of homework (p < .05 for A vs B and C).
Wolfson & Carskadon (1998)³⁵ 1994	Cross-sectional (students in 4 schools in 3 public school districts)	3120	Grades 9–12	Rhode Island	7:10 – 7:30	School Sleep Habits Survey (study, work, sleep, and school habits and preferences)	Students at school with earliest SST (7:10) reported earlier rise times than students at the other schools (p < 0.001). Other sleep related differences did not meet effect size criterion.
Baldus (2002)⁶³ Not specified	Longitudinal (before vs after SST change)	31 (same recruits, 2 sleep schedules)	US Navy recruits (mean 21.3 years)	Great Lakes, Illinois	Early reveille: 9PM-5AM sleep time Late reveille: 10PM-6AM sleep time	Sleep duration.	Later reveille associated with longer sleep duration (p = .01). The 10PM bedtime—6AM rise time resulted in 22 more minutes of sleep per night per recruit.
Wahlstrom (2002)⁵⁵ 1994–2000	Longitudinal (before vs after SST change)	>12 000 (7 HS)	Grades 9–12	Minneapolis, Minnesota	Pre-change: 7:15 Post-change: 8:40	Class grades, attendance, tardiness, graduation rates, rates of continuous enrollment.	After SST change, % continuously enrolled increased (p < .05), attendance rates increased (among students not continuously enrolled) (p < .001), and letter grades increased slightly (not significant).
Wahlstrom (2002)⁵⁵ 1997–2001	Cross-sectional (Minneapolis HS vs District B)	467 (Minneapolis HS) 169 (District B)	Grades 9–12	Minneapolis, Minnesota	Minneapolis HS: 8:40 District B: 7:30	School Sleep Habits Survey³⁵ (study, work, sleep, and school habits and preferences).	Later SST corresponded to longer sleep duration (p < .001), same bedtime, and later rise time (p < .001). Later SST also associated with less daytime sleepiness (p < .01), less struggling to stay awake during academic tasks (p < .01), fewer tardies (p < .01)/absences (p < .05), less falling asleep in morning classes (p < .001), and fewer depressive symptoms (p < .05).
Dexter et al. (2003)⁷³ 2002	Cross-sectional (2 schools with different SSTs)	193 (School 1) 587 (School 2)	Grades 10–11	Altoona (1) and Chippewa Falls (2), Wisconsin	School 1: 7:50 School 2: 8:35	Weeknight sleep duration, Epworth Sleepiness Scale⁹¹.	Mean weeknight sleep duration was longer in School 2 compared to School 1 (p = .039).
Arlington Public Schools (2005)⁸¹ 2000–2002	Longitudinal (before vs after SST change)	3 HS, 5 MS	Grades 7–11	Arlington County, Virginia	HS: 7:30 (2000–2001), 8:15 (2001–2002) MS: 8:10 (2000–2001), 7:50 (2001–2002)	Academic grades (1st period), attendance, survey of students’ perceptions of how alert and prepared to start school day, survey of teachers’ perceptions of student behavior. Surveys were conducted in 2002 only. Respondents were asked to recall prior to SST changes.	10th grade students’ 1st period grades improved after 45 minute SST delay (p < .001), but attendance appeared to decrease. No significant change in 7th grade students’ 1st period grades after 20 minute SST advance.
Adam et al. (2007)⁶⁸ 2002–2003	Cross-sectional	2454	5–z19 years	Nationally (USA) representative	NR	Sleep duration, bedtime, rise time (weekdays and weekends).	For older children (12–19 years), an hour later SST was associated with 0.57 hour more weekday sleep (p < .01), a 0.62 hour later rise time (p < .01), and no difference in bedtime.
Wolfson et al. (2007)⁶⁴ 2003–2004	Cross-sectional (2 schools with different SSTs)	205	Grades 7–8	Urban New England school district	Early school: 7:15 Late school: 8:37	School Sleep Habits Survey³⁵ (sleep duration, bedtime, rise time—weekdays and weekends, sleepiness, sleep-wake behavior problems, sleep hygiene scale), official academic performance, attendance, tardiness.	Late SST associated with later bedtimes (in autumn only) (p < .05), later rise times (p < .001), longer sleep duration (65 minutes) (p < .001), less weekend oversleep (in autumn only)(p < .001), less daytime sleepiness in the autumn (p < .05), fewer sleep-wake behavior problems in the spring (p < .05), higher grades (8th grade only) (p < .01), and fewer tardies (p < .001). Weekend sleep patterns were similar.
Danner and Phillips (2008)⁷⁴ 1998–1999	Longitudinal (before vs after SST change)	9966 (Year 1) 10 656 (Year 2). Sample size included HS and MS students, but results only presented for HS students.	Grades 6–12	Kentucky	Year 1 (Y1): 7:30 (HS) Year 2 (Y2): 8:30 (HS)	Bedtime and rise time (weekdays and weekends), number of naps, Epworth Sleepiness Scale⁹¹, how time spent before and after school, motor vehicle crash rates among 17- and 18-year-old students.	Compared to Year 1, in Year 2 students reported longer average sleep duration (p < .001), less catch- up sleep on weekend nights (p < .001), and lower scores on the Epworth Sleepiness Scale (p < .001). Crash rates in the study county decreased after the SST delay (p < .01).
O’Malley and O’Malley (2008)⁵⁶ 2001–2004	Longitudinal (before vs after SST change)	297 (pre-delay) 977 (post-delay)	Grades 9–12	Wilton, Connecticut	Pre-delay: 7:35 Post-delay: 8:15	Condensed School Sleep Habits Questionnaire³⁵.	Later SST corresponded to longer weeknight sleep duration (p < .001), later rise time (p < .001), later bedtime (p = .03), and fewer problems with sleepiness (p < .001).
Owens, Belon, Moss (2010)⁶⁵ 2008–2009	Longitudinal (before vs after SST change)	201 (mostly boarders)	Grades 9–12	Rhode Island	Pre-change: 8:00 Post-change: 8:30	Bedtime and rise time (weekdays and weekends), sleepiness-related behaviors, health center visits, absences/tardies.	Delayed SST associated with longer school night sleep durations (p < .001), earlier bedtimes (p < .001), later rise times (p < .001), greater sleep satisfaction (p < .001), less sleepiness (p < .001), less sleepiness-related behaviors (p < .001), less depressed mood (p < .001), fewer visits to health center for fatigue-related symptoms (p = 0.03), and fewer absences/tardies (p < .05).
Zhang et al. (2010)⁶⁶ Not specified	Cross-sectional	4470 (mother- father-child community based trios)	Mean age 9.2 ± 1.8y	Hong Kong	Morning school: ~7:35 Whole-day school: ~8:08 Afternoon school: ~12:54pm	Bedtime, rise time, time-in-bed (weekday, weekend, & long holidays), napping	Students in morning schools (earliest SST) had earliest bedtimes & rise times, shortest time-in-bed, most weekend sleep compensation, and largest proportion of daytime napping.
Carrell et al. (2011)⁵⁸ 2004–2009	Cross-sectional	6165	U.S. Air Force Academy freshmen	Colorado Springs, Colorado	Early (2004–2005, 2005– 2006): 7:00. Middle (2006– 2007): 7:30. Late (2007– 2008, 2008–2009): 7:50. For each schedule, some students had a first period class while others did not.	Academic grades by scheduling characteristics.	Students assigned to a first period course had poorer grades; however, this association became weaker and became statistically insignificant as the start time moved from 7:00 AM to 7:50 AM. Students performed worse in first period classes compared to other periods, but those with first period classes also performed worse in their subsequent classes on that schedule day.
Hinrichs (2011)⁵⁹ 1993–2002	Cross-sectional (primarily, but with a longitudinal component)	196,617 observations (may include repeat test takers) (students from 73 schools)	Grades 10–12	Twin Cities metropolitan area (Minneapolis-St. Paul, Minnesota)	7:15–8:40	ACT scores, attendance rates	No association between SST and ACT scores or attendance rates.
Hinrichs (2011)⁵⁹ 2000–2006	Cross-sectional	Approximately 400 public high schools	Grades 10–12	Kansas (public high schools in the state)	Mean (SD): 7:59 (0:15)	School-level test score data on Kansas Mathematics Assessment, Reading Assessment, Science Assessment, and Social Studies Assessment.	No association between SST and scores on reading, mathematics, science, and social studies assessments.
Hinrichs (2011)⁵⁹ 2000–2007	Cross-sectional	75 schools	Grades 9–12? (not specified in report, but described as high schools)	Virginia suburbs of Washington D.C.		Scores on standardized end-of-course exams.	No association between SST and test scores.
Lufi et al. (2011)⁷⁰ Not specified	Longitudinal (before vs after SST change—short term change only)	47	Grade 8	Israel	Early class: 7:30 Late class: 8:30	Sleep duration, bedtime, rise time, sleep efficiency (data from electronic wrist monitors), attention tests.	Later SST associated with longer sleep duration (p < .01) and improved attention (p < .01).
Ming et al. (2011)³⁸ Not specified	Cross-sectional	1941 (students from 2 public high schools, 1 vocational high school, and two extracurricular high school programs whose students came from various high schools throughout the state)	Grades 9–12	New Jersey	Varied from 7:00 to 8:45 For analyses, early SST (before or at 7:30) vs late SST (after 7:30)	Sleep duration, bedtime, rise time, napping, perceived sleep adequacy, night awakenings, prolonged sleep onset	Early SST associated with short weekday sleep duration (<7 hours, p < .0001), lower likelihood of receiving adequate night sleep (p < .0001), and higher likelihood of afterschool naps (p < .0001) and night awakenings (p =NR).
Vorona et al. (2011)⁸⁷ 2007–2008	Cross-sectional (2 cities with different SSTs in public schools)	NR	16–18 years	Virginia Beach and Chesapeake, Virginia	Early schools (Virginia Beach): 7:20–7:25 Late schools (Chesapeake): 8:40–8:45	Motor vehicle crash rates in each city.	Crash rates among 16-to 18-year-olds were higher (p < .01) in Virginia Beach (which has earlier SSTs).
Yilmaz et al. (2011)⁷⁵ 2008	Cross-sectional	3441	15–18 years	Gaziantep, Turkey	Early: 7:00–8:00 (morning) Late: 12:00–12:40 pm (afternoon)	Bedtime, rise time, sleep latency (weekdays & weekends), ideal night sleep time, napping, sleep hygiene	Compared to those with afternoon SSTs, students with morning SSTs reported shorter night time sleep on weekdays and weekends (p < .001) and shorter ideal night time sleep (p < .001). Early SST students were more likely to report daytime napping and needing help to awaken in the morning (p < .001) and less likely to report a long sleep latency (>30 minutes) on weekdays and weekends (p < .001).
Vedaa et al (2012)⁷⁸ Not specified	Cross-sectional	55 students (intervention school) 51 students (control school)	Grade 10	Norway	Intervention school: 9:30 (Mondays), 8:30 (rest of week) Control school: 8:30 (all days)	Karolinska Sleepiness Scale⁹², reaction time tests, Positive and Negative Affect Schedule, sleep diary	Compared to control school students, students at intervention school slept >1 hour longer on Sunday night (p < .05), had a smaller difference between Saturday and Sunday night sleep duration (p = .04), and shorter sleep latency on Sunday night. Students at the intervention school had fewer lapses on reaction time tests (p = .02) and faster reaction times (p = .02) on Monday than Friday compared to the control students. No differences in sleepiness or positive or negative affect.
Edwards (2012)⁵⁷ 1999–2006	Cross-sectional component	20,530 students (1999–2000) 27,686 students (2005–2006)	Grades 6–8	Wake County, North Carolina	7:30–8:45 (53% of students start at 7:30, 22% start at 8:15)	End of year standardized test scores in reading and math; time spent watching television and doing homework; absences	Later SST corresponded to higher standardized test scores on both math and reading tests (1 hour later corresponded to 3 percentile increase), less time watching television, more time doing homework, and fewer absences.
Edwards (2012)⁵⁷ 1999–2006	Longitudinal component (before vs after SST change for schools that changed SST between 1999- 2006)	20,530 students (1999–2000) 27,686 students (2005–2006)	Grades 6–8	Wake County, North Carolina	7:30–8:45 (Some schools started earlier and some started later after SST change)	End of year standardized test scores in reading and math; time spent watching television and doing homework	Later SST corresponded to higher standardized test scores on both math and reading tests (1 hour later corresponded to 2 percentile increase in math and 1.5 percentile increase in reading), less time watching television, and more time doing homework.
Borlase et al (2013)⁶⁹ 1999–2008	Longitudinal (before vs after SST change in 2006)	212 students in Grades 9 and 12 (1999) 455 students in Grades 9, 11, and 12 (2008)	13–17 years	Wellington, New Zealand	Senior students (Grade 12): 9:00 (pre), 10:30 (post) Junior students (Grades 9, 11): 9:00 (no change)	School Sleep Habits Survey³⁵ (study, work, sleep, and school habits, and preferences), technology use, Epworth Sleepiness Scale⁹¹, morningness- eveningness preference, sleep/fatigue problems	Grade 12 students after the SST delay (2008) had longer sleep duration (p < .01), earlier bedtime (p < .01), later rise time (p < .001), less sleep discrepancy (sleep duration on school nights vs. non-school nights)(p < .01), and less sleepiness (p < .01) compared to Grade 12 students before the delay or Grade 11 students (2008).
Li et al. (2013)³⁶ 2007–2009	Cross-sectional/ Longitudinal (6 schools before vs after SST change)	525 (baseline) 553 (2-year follow- up)	Grades 4–5 (mean age 10.8y)	Shanghai, China	2 control schools, no change in SST: 7:30 2 schools, intervention 1: 7:30 (pre), 8:00 (post) 2 schools, intervention 2: 7:30 (pre), 8:30 (post)	Sleep duration, bedtime, rise time, daytime sleepiness (Chinese version of Children’s Sleep Habits Questionnaire)	At baseline, students at the 6 schools had similar sleep characteristics. At follow-up, later SST associated with later bedtime (p < .05), rise time (p < .001), longer sleep duration (p < .001), and less daytime sleepiness. Comparing baseline to follow- up, mean sleep duration decreased for students at control schools (no change in SST) but increased for students at intervention schools.
Perkinson-Gloor et al. (2013)³⁴ 2010–2011	Cross-sectional	2373 (early) 343 (delayed start)	Grades 8–9	Mid-size city in northwestern Switzerland	Early: not specified Delayed: 20 minutes later	Sleep duration, bedtimes, rise times (weekdays and weekends), daytime sleepiness, behavioral persistence, attitude towards life, school grades (mathematics and German language).	Later SST associated with longer weeknight sleep duration (p < .001), later weeknight bedtimes (p = .04 boys, p < .001 girls), later weekday rise times (p < .001), and less daytime sleepiness (p < .001 boys, p = .03 girls).
Short et al. (2013)⁷⁶ 1997–2000 (U.S.) 2008–2010 (Australia)	Cross-sectional	302 (U.S.) 385 (Australia)	Grades 9–12 (mean age 16.0y) (U.S.) Years 9–11 (mean age 15.6y) (Australia)	Rhode Island (U.S.) South Australia (Australia)	U.S.: ~7:45 Australia: 8:20–9:00	School Sleep Habits Survey³⁵ (study, work, sleep, and school habits and preferences), 8-day sleep diary	School night sleep duration correlated with SST (r = .29, p < .001). SST had largest effect on sleep duration (compared with parent-set bedtimes and extra-curricular load).
Boergers, Gable, and Owens (2014)⁶⁷ 2010–2011	Longitudinal (before vs after SST change)	197 (boarding students)	Grades 9–12	Rhode Island	Pre-delay: 8:00 Post-delay: 8:25	School Sleep Habits Survey³⁵ (study, work, sleep, and school habits and preferences), caffeine intake questionnaire	After SST delay, mean wake times (school days) were later (p < .001), mean school night sleep duration was longer (p < .001), school night bedtimes did not change. The percentage who slept ≥8 hour on school nights increased from 18% to 44% (p < .001). There were no changes in nonschool night sleep patterns. After delay, sleepiness scores (p < .001), depression scores (p < .001), and caffeine use decreased (p < .05). No changes in number of hours engaged in athletics, extracurricular activities, and homework were reported. No changes in self-reported grades were reported. Weekday sleep duration decreased to baseline after reverting to pre-delay SST.
Escribano & Diaz-Morales (2014)⁷⁷ Not specified	Cross-sectional (students in 3 schools)	669	12–16 years	Madrid, Spain	8:00, 8:15, 8:30	Bedtimes, rise times, sleep duration, attention task (at 3 times during school day on 2 consecutive Wednesdays), morningness/eveningness, inductive reasoning	Average school night sleep was more than 30 minutes longer for 8:30 SST than 8:00 SST (p < .001). Attention level highest for 8:15 SST on first Wednesday (p < .001), but no difference by SST on second Wednesday. Inductive reasoning score was lowest for 8:30 SST (p < .01).
Chen et al. (2014)⁷⁹ 2009	Cross-sectional	4801 (students from 12 senior HS and 12 junior HS)	11–20 years	Shanghai, China	Dichotimized: Before 7:00 vs. 7:00 or later	Adolescent Sleep Wake Scale⁹³, bedtimes, wake-up times, sleep duration (weekdays & weekends), parents’ sleep habits	SST before 7:00 associated with sleeping <8 hours (p = .015).
Vorona et al. (2014)⁸⁸ 2009–2011	Cross-sectional (2 counties with different SST in public schools)		16–18 years	Chesterfield County, Virginia and Henrico County, Virginia	Early (Chesterfield): 7:20 Late (Henrico): 8:45	Weekday motor vehicle crash rates during the school years (September- May) 2009–2010 and 2010–2011.	In 2009–2010, crash rates among 16–18 year olds were higher (p < .05) in Chesterfield County (which has earlier SST). In 2010–2011, crash rates among 16–17 year olds were higher (p < .05) in Chesterfield County, but difference was not statistically significant when 18 year olds were included in comparison (p = .09). Adult crash rates for the same time periods did not differ between the two counties.
Milic et al. (2014)⁸⁰ 2011	Cross-sectional	821 (students from 4 HS)	15–19 years	Osijek, Croatia	Early: 7:00 AM or 1:00 PM (alternating weeks) Late: 8:00 AM or 2:00 PM (alternating weeks)	Epworth Sleepiness Scale⁹¹, morningness/eveningness, napping, academics (final semester grade)	Students with earlier SST performed better academically and had earlier chronotypes (morning preference) (p < .001). No difference in sleepiness.
Wahlstrom et al. (2014)⁶¹ 2011–2013	Cross-sectional	9089	Grades 9–12	5 HS in Minnesota, 2 HS in Colorado, 1 HS in Wyoming	After delay, SST varied from 8:00 to 8:55	Sleep duration, bedtimes, rise times (weekdays and weekends), sleep-related tardiness, sleeping during class.	SST associated with percent of students sleeping ≥8 hours/school night (R² = .8878, <50% for schools starting before 8:30, 66% for school starting at 8:55).
Wahlstrom et al. (2014)⁶¹ 2011–2013	Longitudinal (before vs after SST change)	446 (pre-delay) 459 (post-delay)	Grades 9–12	Jackson Hole, Wyoming	Pre-delay: 7:35 Post-delay: 8:55	Sleep duration, bedtimes, rise times (weekdays and weekends).	Average school night sleep increased from 7.5h to 8.2h. Average weekend sleep decreased from 9.3h to 9.0h.
Wahlstrom et al. (2014)⁶¹ 2004–2013	Longitudinal (before vs after SST change)	NR	Grades 9–12	5 HS in Minnesota, 2 HS in Colorado, 1 HS in Wyoming	Before delay, SST varied from 7:30 to 7:50 After delay, SST varied from 8:00 to 8:55	Attendance, academic performance, car crashes.	Most schools saw a decrease in tardiness and an increase in GPA. Two out of the four areas for which car crash data was available saw a major decrease in car crashes involving 16- to 18-year-old drivers (≥65%). One saw a small decrease (6%), while another saw a small increase (9%).
Paksarian et al. (2015)⁷¹ 2001–2004	Cross-sectional	7216 (245 schools)	13–18 years	Nationally (USA) representative	Mean: 8:01 Range: 7:05–9:22	Weeknight bedtime, sleep duration (weeknight and weekend), weekend compensatory sleep	Later SST associated with later bedtime (10 minute later bedtime for each 30 minute delay in SST). Later SST associated with longer sleep duration for SST before 8:01 only (11 minutes for each 30 minute delay in SST). Difference only among boys only and varied by urbanicity. Sleep duration increased for boys in major metropolitan areas and decreased for boys in nonurban counties. SST not associated with weekend compensatory sleep.
Only Abstracts Available
Allen and Mirabile (1989)⁵⁰ Not specified	Cross-sectional	61	Grades 10–12 (Mean age 17.1 years)	NR	Early school: 7:30 Late school: 8:00	Sleep duration, bedtimes, rise times (weekdays and weekends).	Later SST corresponded to later rise times (p < .05), but no difference in bedtimes. Sleep duration difference not significantly different.
Allen (1992)⁵¹ Not specified	Cross-sectional	102	Grade 12	NR	Early school: 7:40 Late schools: 8:30	Sleep duration, bedtimes, rise times (weekdays and weekends).	Earlier SST corresponded to shorter weeknight sleep duration (p < .035), more sleep problems (p = .04), and later weekend rise times (p = .03).
Carskadon et al. (1995)⁵³ 1994	Longitudinal (before vs after SST change)	7	Grade 9–10	Rhode Island	Late (Grade 9): 8:25 Early (Grade 10): 7:20	Sleep duration, sleep start time, sleep offset time (measured with actigraphy)	Earlier SST (65 minutes) corresponded to shorter sleep duration (38 minutes, p < .02) due to earlier rise times (59 minutes, p < .005). No significant difference in school night sleep start time.
Kowalski and Allen⁵² Not specified (1995)	Cross-sectional	97 (early school) 119 (late school)	Grades 11–12	NR	Early school: 7:20 Late school: 9:30	Sleep duration, bedtimes, rise times (weekdays and weekends).	Earlier SST corresponded to shorter weeknight sleep duration (p = .002).
Wolfson et al. (1995)⁵⁴ 1994	Longitudinal (before vs after SST change)	15 (May have included students in Carskadon et al.⁵³)	Grade 9–10	Rhode Island	Late (Grade 9): 8:25 Early (Grade 10): 7:20	Sleep duration, sleep start time, sleep efficiency (measured with actigraphy); emotional/behavioral problems from Youth Self Report (YSR) summary.	Earlier SST (65 minutes) corresponded to shorter sleep duration (39 minutes, p < .001). No significant difference in school night sleep start time or sleep efficiency. YSR total problems and externalizing scores decreased with earlier SST.

Abbreviations: ACT, originally American College Testing – one of two standardized tests commonly used in college admissions in the United States; HS, high school; MS, middle school; NR, not reported; SD, standard deviation; SST, school start time.