McKeever, P. M., Clark, L. (2017). Delayed high school start times later than 8:30 am and impact on graduation rates and attendance rates. Sleep Health, 3(2), 119-125. 

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Abstract
Objectives
The first purpose of this study was to investigate changes in high school graduation rates with a delayed school start time of later than 8:30 am. The second aim of the study was to analyze the association between a delayed high school start time later than 8:30 am and attendance rates.

Design
In the current study, a pre-post design using a repeated-measures analysis of variance was used to examine changes in attendance and graduation rates 2 years after a delayed start was implemented.

Setting
Public high schools from 8 school districts (n = 29 high schools) located throughout 7 different states. Schools were identified using previous research from the Children's National Medical Center's Division of Sleep Medicine Research Team.

Participants and Measurements
A total membership of more than 30,000 high school students enrolled in the 29 schools identified by the Children's National Medical Center's Research Team. A pre-post design was used for a within-subject design, controlling for any school-to-school difference in the calculation of the response variable. This is the recommended technique for a study that may include data with potential measurement error.

Results
Findings from this study linked a start time of later than 8:30 am to improved attendance rates and graduation rates.

Conclusions
Attendance rates and graduation rates significantly improved in schools with delayed start times of 8:30 am or later. School officials need to take special notice that this investigation also raises questions about whether later start times are a mechanism for closing the achievement gap due to improved graduation rates.

Keywords
Delayed school start times, High school bell times, Attendance rates, Graduation rates, Graduation completion, Inadequate sleep, Insufficient sleep, Adolescent sleep, Student social–emotional health