SACRAMENTO, Calif. >> The bell doesn’t ring until 8 a.m. at Lincoln High School, but by then freshman Briana Lopez has been awake for hours.

The 14-year-old leaves her house in Northern California at 6:30 each morning so she can get to school for a 7 a.m. marching band practice. On Mondays, she has a second practice after school that does not end until 9 p.m.

“I say, ‘You have to go to bed by 9,’ but at 10 o’clock she is taking a shower sometimes,” said Teresa Favila-Lopez, the teen’s mother. “School is insane. It wasn’t like that when I was in school.”

Worried about the ill effects of sleep deprivation for students, California on Sunday became the first state to mandate a school start time under a new law signed by Gov. Gavin Newsom. Beginning in the 2022 school year, high schools in the nation’s most populous state can’t start before 8:30 a.m. and middle schools can’t start before 8 a.m.

It’s a big victory for the “start school later” movement, which has been pushing districts to adjust their daily calendars for decades in the name of public health.

“We think of it as almost a joke, that teenagers are always crabby in the morning and they stay up way too late,” said Celia Jaffe, president of the California State PTA, which supported the law. “It’s better for their mental health, it reduces depression and other mental health problems.”

Teachers and school districts warn that the law will burden them with unexpected expenses, like changing bus routes and paying staff to chaperone students who still must arrive early because of their parents’ work schedules.

“Often working families have strict schedules with less work flexibility and they won’t always be able to accommodate them in a way that’s necessary to make late start times work,” said Troy Flint, spokesman for the California School Boards Association, which opposed the law.

Many students might still need to start classes earlier. The new law does not affect “zero periods” — classes that begin before the school day. Plus, many students have sports and band practices before school, although it’s possible those activities could start later to coincide with the delayed school start time.

In California, the average start time for middle and high schools was 8:07 a.m. in 2011, according to the latest figures available from the U.S. Centers for Disease Control and Prevention.

More than 78% of those students started before 8:30 a.m.

The National Center for Education Statistics said 7:59 a.m. was the average start time for public high schools in the U.S. in 2011.

In the Elk Grove Unified School District, outside Sacramento, high school start times vary based on traffic patterns and how far students live from the school, according to Communications Director Xanthi Pinkerton. Laguna Creek High School starts at 7:45 a.m., while Elk Grove High School starts at 8 a.m.

Pinkerton said the district believes school start times should be decided by local officials, not the state.

Some school officials are confused about how to implement the law, which exempts “rural school districts” but does not define what that means. It’s an issue that state regulators must resolve by 2022.

Democratic state Sen. Anthony Portantino, who authored the law, noted in a news release, “now our work begins to implement this necessary educational and public health reform.”

The American Academy of Sleep Medicine says teenagers should get eight to 10 hours of sleep each night. Teens that don’t are more likely to be overweight, have depression symptoms and engage in risky behavior such as drinking, smoking and using illegal drugs.

Academic research is split on whether starting school later improves students’ grades. A policy statement from the American Academy of Pediatrics noted “academic achievement with delayed start times have been somewhat less consistently demonstrated.”

In 2016, the Seattle School District changed its start times from 7:50 a.m. to 8:45 a.m. for high schools and most middle schools. Researchers reported the change resulted in an extra 34 minutes of sleep per night for students but did not have conclusive results about how the extra sleep impacted grades.

Lopez, a clarinet player in the Lincoln High School marching band, said she welcomes the new law. It won’t take effect until her senior year, but right now, when she’s getting up “at 5ish” for a 7 a.m. band practice, she dreams about an extra 30 minutes of sleep.

“It’s really hard getting up in the morning and getting ready for school and getting your mind ready for school,” she said.