Today the Centers for Disease Control and Prevention published a new report analyzing state-specific distributions of public middle and high school start times. The report is published online in the Aug. 7, 2015, issue of the CDC’s Morbidity and Mortality Weekly Report.

Results show that among an estimated 39,700 public middle, high, and combined schools in the U.S., the average start time was 8:03 a.m. Overall, only 17.7% of these public schools started school at 8:30 a.m. or later.

“Early start times for high school classes can interfere with teens’ natural biological clocks, resulting in a lack of adequate sleep for many adolescents,” said American Academy of Sleep Medicine President Dr. Nathaniel Watson. “Implementing smarter school start times that are more consistent with teens’ sleep needs can improve students’ safety, overall health, mood and academic performance.”

The percentage of schools with 8:30 a.m. or later start times varied greatly by state, ranging from 0% in Hawaii, Mississippi, and Wyoming to more than three quarters of schools in Alaska (76.8%) and North Dakota (78.5%). Louisiana had the earliest average school start time (7:40 AM), while Alaska had the latest (8:33 AM). The results are based on an analysis by the CDC and the U.S. Department of Education of data from the 2011–12 Schools and Staffing Survey (SASS).

An AASM health advisory on teen sleep duration and school start times recommends that adolescents get a little more than nine hours of nightly sleep for optimal health and daytime alertness during the critical transition from childhood to adulthood. However, CDC data show that less than 10 percent of high school students report sleeping 9 or more hours on an average school night.

The AASM notes that in puberty a natural shift occurs in the timing of the body’s internal “circadian” clock, causing most teens to have a biological preference for a late-night bedtime. The AASM recommends that parents and local school boards work together to implement high school start times that allow teens to get the healthy sleep they need to meet their full potential.

The CDC report notes that school start times are determined at the district or even individual school level, which means that local stakeholders have the most influence on whether start times change in their communities. According to the CDC, among the possible public health interventions for increas¬ing sufficient sleep among adolescents, delaying school start times has the potential for the greatest population impact by changing the environmental context for students in entire school districts.

Read the CDC report: School Start Times for Middle School and High School Students — United States, 2011–12 School Year