. 2017 Jul 3;2017(7):CD009467. doi: 10.1002/14651858.CD009467.pub2

Summary of findings for the main comparison. Early versus delayed school starts.

Early versus delayed school starts
Patient or population: students aged 13‐19  Setting: Canada (Toronto), USA (Colorado, Rhode Island, Minnesota, Kentucky, North Carolina, Wyoming), northern Israel, New Zealand (Wellington), Croatia, and southern Brazil  Intervention: later school start times (08:00, 08:45, 09:00, 10:00, or 10:30; start time delayed by 60‐90 minutes)  Comparison: early school start time (07:00, 07:15, 07:20, or 07:30)
Outcomes	Impacts	№ of Participants (studies)	Quality of the evidence  (GRADE)
Student academic outcomes	There is no clear association between later school start times and student academic outcomes, as two studies reported significant positive associations (b = 1.78, b = 0.98; effect sizes could not be calculated from one study), one study reported a non‐significant negative association (b = −0.02), and one study reported a significant negative association (MD −0.32 GPA points on a scale of 0 to 4, with higher GPAs indicating better grades).	254,743 (4)	⊕⊝⊝⊝  Very low^a
Amount or quality of sleep	All studies that evaluated the association between later school start times and amount or quality of sleep reported significant positive associations, providing evidence that later school start times are associated with increased sleep (effect sizes ranged from MD 0.49 to 1.95 hours) and lower risk of losing sleep (RR 0.41).	52,340 (8)	⊕⊝⊝⊝  Very low^a
Mental health outcomes	There is limited evidence concerning the association between later school start times and mental health outcomes: one study reported significant differences in self‐reported depression symptoms for students in later starting schools (07:25 and 08:30) than earlier starting schools (07:15), but no significant difference between students starting school at 08:30 vs 07:25.	1200 (1)	⊕⊝⊝⊝  Very low^a
Truancy or attendance outcomes	There is mixed evidence concerning the association between later school starts and attendance outcomes: one study reported a significant increase in attendance, one study reported a non‐significant increase in attendance, and one study reported a significant increase in attendance for 2 of 6 schools and non‐significant effects (no further information provided) for the other 4 schools.	255,122 (4)	⊕⊝⊝⊝  Very low^a
Alertness	There is mixed evidence concerning the association between later school starts and student reports of alertness or sleepiness. Two studies found an association between later school start times and decreased daytime sleepiness, while one study found no difference between student reports at later and earlier starting schools. One study reported a significant increase in attention levels but a non‐significant increase in concentration levels.	2735 (4)	⊕⊝⊝⊝  Very low^a
Adverse events/unintended consequences	Authors provided limited information concerning adverse events and unintended consequences but did offer that later school start times may be associated with decreased morning interactions between parents and children, decreased alertness in mid‐afternoon, and increased logistical challenges, including missing extracurricular activities, transportation troubles, and safety concerns (as students may have to walk home in the dark).	207,576 (4)	⊕⊝⊝⊝  Very low^a
b: regression coefficient; CI: confidence interval; GPA: grade point average; MD: mean difference; RR: risk ratio
GRADE Working Group grades of evidence   High quality: we are very confident that the true effect lies close to that of the estimate of the effect.  Moderate quality: we are moderately confident in the effect estimate: the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different.  Low quality: our confidence in the effect estimate is limited: the true effect may be substantially different from the estimate of the effect.  Very low quality: we have very little confidence in the effect estimate: the true effect is likely to be substantially different from the estimate of effect.

^aDowngraded one level (from starting point of 'low' for observational study designs). The GRADE rating of 'very low' for all findings reflects study designs (absence of RCTs), high risk of bias within the studies, and inconsistency within the estimates.