The measure would become effective by July 1, 2022.

California has become the first state in the country to push back start times at most public schools in the hope the measure will help adolescents perform better in class.

The new law signed on Sunday by Governor Gavin Newsom calls for middle schools to ring in classes no earlier than 8:00 am and high schools no earlier than 8:30 am.

The measure would become effective by July 1, 2022 or when a school district's three-year bargaining agreement that is operative on January 1, 2020, expires.

Most California schools currently start the day around 8:00 am and some require students to be in class before 7:30 a.m.

"The science shows that teenage students who start their day later increase their academic performance, attendance and overall health," Newsom said in a statement.

"Importantly, the law allows three years for schools and school districts to plan and implement these changes."

While the measure has received backing from several medical associations, including the American Academy of Pediatrics and the California Medical Association, the bill has run into opposition by some lawmakers and school districts.

"We can all agree that our students need a sufficient amount of sleep, and that sleep time is a significant and important factor in overall health, but improving sleep time for students requires more than just later start times," state senator Connie Leyva told the Sacramento Bee.

"I believe that school start times should continue to be determined at the local level, because it is inappropriate to say that a one-size-fits-all approach should guide all schools or all communities."

Leyva and other critics also noted that the time change will prove to be a hardship for many working parents who may not be able to adjust their schedules.

Janet Napolitano, president of the University of California, said the state would do better to carry out a pilot study on later start times before imposing it on school districts.

"As much as I sympathize with sleepy students, we must also carefully consider how the change would affect families and schools," she said.

According to numerous studies, there is a link between the amount of sleep adolescents get and school performance.

The American Academy of Pediatrics says it "recognizes insufficient sleep in adolescents as an important public health issue that significantly affects the health and safety, as well as the academic success, of our nation's middle and high school students."