Troy Flint, spokesman for the California School Boards Association, said the updated rule "is a huge difference in terms of how districts would operate and how the public is going to receive this guidance."
The rule could also force districts into some tough decisions. All California schools are required to resume in-person instruction when the new school year starts, but the new rules also require districts to provide remote learning options to students if officials send them home for refusing to wear masks.
"If you have a district that chooses to take a harder line on masking and a subset of parents that doesn't want to comply, the school is obligated to provide independent study in a really robust way that asks more of the district than has been done in the past," Flint said.
In a new set of guidelines released last week, the Centers for Disease Control and Prevention said teachers and students who are fully vaccinated don’t have to wear masks indoors but recommended that students and staff stay at least 3 feet apart to reduce the spread of a disease that is primarily transmitted through the air.
State officials, however, were worried that imposing social distancing would make it harder for some schools to accommodate all students. So they chose to not require physical distancing in exchange for universal mask-wearing, a precaution they said would also help prevent the spread of new strains of the virus, like the delta variant.
The new state guidelines additionally recommend, but don't require, that older students get vaccinated. They also strongly urge schools to limit non-essential visitors, have their students eat lunch outdoors when possible and utilize the state's free COVID-19 testing resources.
Dr. Naomi Bardach, a UCSF pediatrician who heads the state’s Safe Schools for All plan, said the CDC's looser school mask guidelines are problematic in that they reinforce a divide between vaccinated and unvaccinated students.
"The way the CDC guidance is written, it says vaccinated students don't have to wear masks and unvaccinated students have to wear a mask. And so that allows, all of a sudden, for two classes," Bardach said. "And it really opens up the possibility of stigma, of bullying."
Two-thirds of California public school students 12 and older are not fully vaccinated, according to Bardach, who stressed that requiring everyone to wear masks will make schools much safer and simplify enforcement for school officials.
"And so we actually would like to allow schools to open in a way that is a less controversial environment for those students as they walk through the doors," she said.
The state's mask requirement, though, angered some parents who say it will create additional stress for children who have already had two school years upended through remote learning and missed milestones like proms, sports, concerts and graduations.
"We’re continuing to put the burden of this pandemic on our children, and it needs to stop," said Jonathan Zachreson, a father of three and founder of the group Reopen California Schools.
Newsom faced heavy criticism for not moving more quickly to return students to classrooms during the last school year. Many districts, including Los Angeles, with more than 550,000 K-12 students, only instituted part-time, in-person instruction for the final weeks of the spring semester.
Dr. Monica Gandhi, an infectious disease specialist and professor of medicine at UCSF who has advocated for California to loosen mask guidelines for fully vaccinated people, said the state's new school mask rules seemed reasonable.
She said that while eliminating the physical distancing requirement is one of the best things the state can do to get kids back in classrooms, the mask-requirement question is still a gray area because there is so little data about children.
"We’ve just got to get the kids back and then we can sort out those kinds of details," Gandhi said.
But Dr. Jeffrey Klausner, a clinical professor of population and public health sciences at the University of Southern California, said the rules go too far and are not based on local data. He said it's unreasonable "in a state of 40 million people, just to say everyone has to be the same."
"I think they’d have better trust and credibility with Californians if they were a little more nuanced and smarter about it," he said.