At Clark Avenue Middle School in Chelsea, there's this surprising sight: students sitting at desks, in a community with one of the highest COVID-19 infection rates in Massachusetts.

They come to school to put on their headphones and log into classes remotely. Like a silent rave, a dozen classes occur simultaneously, but the room is mostly quiet.

“It’s a place where parents know, just like sending them to school, that it’s a safe place,” said Michael Talbot, Clark Avenue's principal.

If students can go into a school building in Chelsea with masks and social distancing, are schools safe? A growing body of research, mostly from overseas, has shown that they are, leading Gov. Charlie Baker to urge schools statewide to adopt remote learning only as a last resort. But do not expect schools to fling open their doors open any time soon.

The calculus around school safety ultimately rests with the priorities of elected state and local leaders.

William Hanage, a professor of epidemiology at Harvard's T.H. Chan School of Public Health, said the current scientific consensus is that children up to age nine are less likely to become infected with the virus. It’s not clear, however, if they transmit it to others.

Kids ages 10 to 19 are much more likely to become infected and transmit the virus. That means youth can affect household infection rates, which have been shown to be the main source of infection spread in Massachusetts.

The key to opening schools, Hanage says, is to keep overall community transmission rates low. But there is not one way to do that.

“It says something about our priorities if we're talking about closing schools and we're not talking about doing stuff elsewhere to try to curb the virus,” Hanage said. “Schools, ideally, should be the last thing to close and the first thing to reopen.”

Yellow student lockers with a sign asking students to not touch surfaces
A sign in a hallway at the Clark Middle School in Chelsea, Mass. instructs students to avoid touching surfaces as a precaution against the spread of the novel coronavirus.
Meredith Nierman GBH News

In Massachusetts, Baker has allowed casinos, restaurants, and trampoline and paintball parks to remain open, although he has put some restrictions on their operations. And while he has pushed school districts to reopen, Baker has no authority over locally-controlled school districts, and the state’s instructions to schools are strictly “guidance.”

State officials say they deploy a mobile COVID testing unit to a school if a cluster — when at least two or more cases are associated with the same location — is suspected. As of Nov. 20, the unit has been deployed to 13 different schools in 12 communities.

The Department of Elementary and Secondary Education says not many instances of transmission within school settings have been confirmed. It did not disclose those locations.

"There [have] been very limited instances of in-school transmission in Massachusetts public schools, even in communities with higher COVID-19 transmission rates,” Colleen Quinn, a spokeswoman for the Executive Office of Education, said in a statement to GBH News. “Only a few clusters out of thousands have been associated with transmission in school settings, and these have been small and limited in nature.”

At the same time, infections in public schools statewide have risen sharply. Between Nov. 11 and 18, schools reported their highest infection rates ever: 398 students in-person (full- and part-time or hybrid) reported testing positive, more than double the number from the week before. And 254 staffers became infected, up from 157. By comparison, those case numbers were 61 and 35, respectively, in the last week of September.

Earlier this month, the state alsoreconfiguredthe way it calculates community infection rates, which made fewer cities and towns red, even as rates rise dramatically around the state.

Carlene Pavlos, executive director of the Massachusetts Public Health Association, said the state has seen a seven-fold increase in infections since September. She's concerned that some school districts that shifted from the state's red to green designation will be more lax about precautionary measures, potentially causing the virus' spreading to worsen.

“It is time to really think about the kinds of policies that need to be in place to keep transmission rates low,” Pavlos said. “What we’re doing right now is clearly in the opposite direction from reducing community transmission rates.”

Last week, The Lowell Sun reported that 11 students at Billerica Memorial High School tested positive for COVID-19, and the school switched to remote learning through Nov. 30. School officials also said they suspected “potential evidence of in-school transmission,” but did not offer further details.

There is no community or school testing program in the Billerica district, about 30 miles northwest of Boston.

Teachers’ unions have been opposed to reopening schools until leaders ensure that buildings are well ventilated and testing is standard practice. Merrie Najimy, president of the Massachusetts Teachers Association, says the state’s recent decision to offer COVID testing in less than half of the state’s school districts is troubling.

“If the governor is saying, 'We care about students’ wellness,' then we can’t put together piecemeal solutions,” she said.

Chelsea School Superintendent Almi G. Abeyta (l) and Clark Middle School Principal Michael Talbot stand outside the main office of the Clark Middle School in Chelsea, Mass. on November 17, 2020.
Meredith Nierman GBH News

In Chelsea, the remote learning center at Clark Avenue Middle School is an improvised solution. It operates in the school cafeteria in the basement. Unlicensed teacher aides supervise the students.

Superintendent Almi G. Abeyta said everyone knows in-person learning is best for students. But she is proud that her district's two remote centers, which opened two months ago, have had only one case of COVID. It is not a small accomplishment in a community where infection rates are seven times higher than places like Newton and Natick.

Students sit in rows at their desks, some with hoods pulled down over their heads as they stare into their Chromebooks. One student sings into his microphone in his music class until he realizes other people can hear him.

"They're coming to school. ... That routine every day,” Abeyta said, “it’s important, and we did want to provide some relief to parents who needed it.”