But on Aug. 30, the 2,800-student district began requiring students to wear masks outside as well as in the building 鈥� and hasn鈥檛 had to send a whole classroom home since. The new policy was prompted by the state鈥檚 revised for unvaccinated students, which allow asymptomatic students to stay in school if they meet several conditions, including wearing masks both inside and outside.

鈥淲e are optimistic it is working,鈥� said Kristie Towne, manager of board and superintendent operations for the Solana district, part of San Diego County. 鈥淭丑别 policy is meant to keep as many children in school [and] in class as much as possible.鈥�

With the recent rise in positive cases due to the more transmissible Delta variant, districts like Solana Beach are now enforcing additional measures 鈥� policies that go beyond recommendations from most state health departments and the which says masks aren鈥檛 needed during recess. The Los Angeles Unified School District was among the first to institute the practice and several other California districts have followed suit. Others as far as Vermont and North Carolina have instituted similar measures but are targeting them to younger students or athletes. One problem: The research behind such moves is pretty thin.

鈥淥utside, there鈥檚 an infinite volume of air to dilute the virus,鈥� said Dr. Dean Blumberg, a pediatric infectious disease expert at the University of California, Davis.

Dr. Benjamin Linas, a Boston University epidemiologist, warns that outdoor masking could even be counterproductive.

鈥淚f there is any hope of successfully implementing masks when we need them 鈥� indoors during Delta surge 鈥� then we cannot insist on masks when we do not need them, and we should not routinely 鈥榬ound up鈥� when not certain,鈥� he said. 鈥淭oo much masking is real.鈥�

Advocacy groups that were already fighting the state鈥檚 mandate that students wear masks indoors argue that requiring them outdoors further hinders children鈥檚 social development.

鈥淥utdoors our kids need to be breathing fresh air. They need to have social interaction and share smiles,鈥� said Sharon McKeeman, who founded and in July filed , with Reopen California Schools, against California Gov. Gavin Newsom, the state health department and other officials. 鈥淭丑别se restrictions are arbitrary, and they are infringing our kids鈥� rights.鈥�

The measures came as some districts faced criticism for quarantining too many students without symptoms.

In August, in Los Angeles and other districts missed class and did not always have access to remote learning. Other California districts requiring masks outside include the 12,000-student Palo Alto Unified School District, where the most shows two cases districtwide, and the 9,600-student , which had 27 cases in August and seven so far in September.

鈥楾he benefits are uncertain鈥�

Some opponents of mask requirements note that the , which President Joe Biden as soon as he became president, doesn鈥檛 recommend masks at all for children 5 and under.

A growing body of research on transmission of the virus shows that the proportion of cases originating outside are well below 10 percent and could be even less than 1 percent, according to a in the Journal of Infectious Diseases.

International studies provide further evidence of significantly low risk. A found that out of 7,300 cases, one outbreak resulting in two cases was linked to an outdoor conversation between two people. An showed that about one in 1,000 cases was due to outdoor transmission.

Most outdoor cases are linked to lengthy interactions between people or crowded events, studies show.

鈥淚 am having a very hard time thinking of when a school would generate such an opportunity for transmission,鈥� Linas said. 鈥淚t is not recess or outdoor classwork. Perhaps if a school had an outdoor pep rally in a relatively small stadium with full bleachers and kids on the field, too. I am struggling to come up with a realistic scenario.鈥�

Experts stress that with the Delta variant, local vaccination rates of those 12 and above should guide decisions about whether additional caution is needed.

That鈥檚 why Andrew Hayes, a school board member in the Lakeside Union Elementary School District in San Diego County, questions the governor鈥檚 inside mask mandate to begin with.

鈥淭丑别 about being at an 80 percent vaccination rate, but we are still having all these mitigation strategies everywhere,鈥� Hayes said. 鈥淚 understand that people want to follow the experts, but they aren鈥檛 allowing the experts in education to make decisions.鈥�

His district has not yet required masks outside, but surrounding districts have.

Hayes is among in California who want to loosen local mask requirements in violation of the statewide mandate requiring students to wear them indoors. The California Department of Public Health on Aug. 23 sent districts stating they could face fines and civil lawsuits if they don鈥檛 enforce masking.

The dynamic is the opposite of that in Florida, where districts mandating masks are locked in a protracted legal battle with a Republican governor who says parents should choose.

California isn鈥檛 the only state where some districts are going above and beyond CDC guidelines, which state: 鈥淚n general, people do not need to wear masks when outdoors鈥� for play, recess and physical education. But other examples are more targeted.

The , near Burlington, Vermont, requires masks outdoors for students in K-5 if they can鈥檛 socially distance. The district is requiring masks outside for elementary and middle school students, and the district in North Carolina requires athletes to wear masks outside when they鈥檙e not actively participating in a game or practice.

In California, McKeeman, with Let Them Breathe, said even in districts that don鈥檛 require students to wear masks outside, 鈥渢here鈥檚 still a lot of enforcement to keep it on anyway.鈥�

Some experts recognize the challenges teachers and other school staff members face when children are constantly taking masks on and off. Blumberg, who said he still wears a mask when he goes to the farmer鈥檚 market, noted that many classroom buildings in the state鈥檚 schools are connected by outside hallways.

For the sake of consistency, he said, 鈥淚t鈥檚 easier to just say, 鈥楳ask while at school and don鈥檛 think about it.鈥欌��