SAN DIEGO — It's the first day of school for kids in the San Diego Unified School District. More than 120 thousand students returned for a new school year Monday.

As part of the district’s "Healthy Start Times" initiative, classes at San Diego School for the Creative and Performing Arts, La Jolla High School, and Muirlands Middle School will begin at 8:35 a.m.

All high schools in the district will have later start times, which will vary anywhere from 8:35 a.m. to 9:05 a.m. beginning in the 2020-21 school year.

Why the move to later start times?

The district says "later start times have been found to increase student attendance, improve academic performance, and most importantly, keep students healthier."

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Insufficient sleep in adolescents has been shown to be associated with a wide variety of adverse outcomes, from poor mental and physical health to behavioral problems and lower academic grades. However, most high school students do not get sufficient sleep. The American School Health Association found:

"Most studies reviewed provide evidence that delaying school start time increases weeknight sleep duration among adolescents, primarily by delaying rise times. Most of the studies saw a significant increase in sleep duration even with relatively small delays in start times of half an hour or so. Later start times also generally correspond to improved attendance, less tardiness, less falling asleep in class, better grades, and fewer motor vehicle crashes."