The nation’s second largest school district, Los Angeles Unified, said Friday it will close schools as coronavirus cases climb in California and the United States. Entire states — Ohio, Maryland, Michigan and New Mexico — have closed schools. 

But until the state stepped in Friday afternoon, Chicago, the third-largest school district in the country, was going to stay open. Why?

Mayor Lori Lightfoot has had to defend her decision to keep Chicago schools open at every public turn. A former federal prosecutor who is used to fielding tough questions, she’s been stoic in her response: She’s assessing and reassessing multiple times a day, she said, but closing schools has “cascading consequences,” as the city saw during an 11-day campus shutdown during last fall’s teachers strike. 

Lightfoot told reporters Friday morning her team has been calibrating and balancing data. “If we get to a point where it is prudent to close schools, we’re going to do that in a way that mitigates and minimizes the burden that we will invariably be placing on households.” 

Related: Find our live blog with updates about coronavirus and Chicago schools here

Until Friday afternoon, Gov. J.B. Pritzker also stopped short of issuing an edict for statewide closures. In Illinois as of Thursday, there were 32 confirmed cases. Lightfoot said the two are in contact multiple times a day on the issue.

“The governor has concerns about schools across the state. We’re having multiple conversations every single day about what we’re doing, why we’re doing what we’re doing, and using data to drive the decision. In the event we need to take action, we will do that in partnership with the state.”

Pressure has been increasing. On Friday, the Chicago Teachers Union called for immediate closures, a day after it had taken a less drastic position and asked the district to close schools temporarily on Election Day, March 17, since many campuses serve as polling places. A closure, it argued, could double as a cleaning day. 

By Friday, the union’s position had changed from calling for a one-day closure on Election Day to reduce student exposure risk to an immediate closure effective Friday, citing concern for frontline workers, from teachers to support staff. “This is the time to be proactive and cautious,” the union’s chief of staff, Jennifer Johnson, said in an interview with Chalkbeat. 

But there are also new questions about the effectiveness of school closures. The Centers for Disease Control and Prevention said in new guidance Friday that short-term closures may not slow the growth curve of the virus.

Here’s how the mayor and the city’s top health official, Allison Arwady, explained their position on Friday.

They believe children to be at low risk of transmitting infection or becoming sick.

Arwady, who is a pediatrician and still sees patients, said Friday that she knew parents had serious concerns about protecting their children. But she reiterated that the risk to children is low. 

“This (virus spread) does not seem to be primarily driven by children,” she said.

At Vaughn Occupational High School, which the district closed this week after an aide tested positive for the novel coronavirus, the city has tested 42 people who reported symptoms and none of the tests has been confirmed positive, she said. 

“It’s possible we could still determine a case of transmission at that school, but I think that’s unlikely at this point. What we know about coronavirus nationally, and internationally … 2.4% of the cases in Chicago have been in children 18 and younger; 98% have been in adults. When children have gotten sick, by and large, they’ve gotten mildly ill.”

She said the data out of China also don’t show large “transmission chains” of children spreading the disease to adults. 

Closing schools is a decision that has serious consequences for working families.

Around 355,100 children attend Chicago public schools, and 78% are considered low-income. “When we close schools that means in a lot of instances that parents have to stay home,” Lightfoot said Friday morning. “In some instances that may mean we’re taking nurses out of hospitals, doctors out of hospitals. We also know that many of our parents are hourly workers and they would have to stay home because of the cost, and or the availability, of childcare. For that population, which is dependent upon paycheck to paycheck to meet the needs of their families, closing schools has cascading consequences.”

Schools provide meals for hungry children and regular shelter for the housing insecure. 

“Many students rely on schools to eat,” the mayor said, echoing a similar reluctance to close schools voiced this week by New York City Mayor Bill de Blasio.

Patricia Nix-Hodes, the director of the law project of the Chicago Coalition for the Homeless, said about 5% of the city’s schoolchildren are homeless or doubling or tripling up with other families. She worries about how closings would affect children. “If schools close, there has to be a plan for addressing food insecurity for homeless students and families and other low-income students who may not be in homeless situations but may also rely on school meals for food.”

The city has concerns about where children will go, and whether grandparents would be put at risk by becoming primary caregivers.

Arwady reiterated Friday that her team is most concerned about the city’s aging population. “There are lots of conversations about schools. We’re not done with those conversations. When we do think about closing schools, when we think about that here, we think about where kids would go. Often they go to grandma. When I’m worried about who’s at risk and who’s moving around, I’m not that sure that is something that makes sense.”

Closing schools early has not proven to slow the curve of the virus, the CDC said Friday.

In revised guidance issued March 13, the Centers for Disease Control and Prevention suggested that early, short- to medium- term closures don’t appear to slow the progression of COVID-19 in a community. Longer closures — eight to 20 weeks — might retard the virus’ community spread, it said. But modeling shows that other recommended measures like handwashing and isolating patients at home could have a greater effect, the federal agency advised.

Places like Hong Kong that closed schools haven’t had more success in reducing the novel coronavirus spread than have areas like Singapore that kept campuses open, the CDC observed.

On the other hand, observers of the COVID-19 epidemic in Italy have emphatically advised early social isolation, including closing schools, to slow down the virus’s progress through communities.

So far, the word from parent advocacy groups on whether to close schools has been mixed. Cassandra Creswell, with the parent advocacy group IL Families for Public Schools, said the governor should close schools statewide, and find workarounds for meal distribution and child care. 

But Jianan Shi, executive director with parent group Raise Your Hand, has a different take. He said that his group was so far on board with the decision to keep schools open as long as it was the recommendation of public health officials. “A lot of students do depend on school for many services,” Shi said. “We want to trust our professionals.” 

Yana Kunichoff and Samantha Smylie contributed reporting. 

Correction: This story has been updated to reflect that about 5% of Chicago’s overall public school enrollment is identified as living in a homeless situation, not 11%. Chalkbeat regrets the error.