Students, teachers, and staff will be required to wear masks in all Pennsylvania schools as the year starts, Gov. Tom Wolf said Tuesday, announcing a mandate prompted by the delta-driven surge of the coronavirus and an increase in cases among children since some schools began opening.

The order, issued by acting Health Secretary Alison Beam and taking effect next Tuesday, covers public and private preK-12 schools as well as licensed child care centers.

“Doing nothing right now to stop COVID-19, that’s just not an option,” the governor said at a news conference in Harrisburg. “Our commonwealth and our nation are in a different place than we were just a month ago. And our students need our help to stay safe and stay in school.”

The mandate is an eleventh-hour reversal for Wolf, who had previously said individual districts could decide how to reopen. He acknowledged the state could have acted sooner but said his administration did so now because fewer than half the state’s school districts had required masking and the Republican-led legislature rejected his call last week to enact a mandate.

How smoothly and broadly it will be followed won’t be clear for days. Wolf and education officials had no plans for enforcing the order, saying that would be up to schools and districts. It also faces possible challenges from lawmakers, parents, or school boards.

Minutes after Wolf’s announcement, House Majority Leader Kerry Benninghoff called the decision an “ill-advised statewide mandate that deprives Pennsylvania communities of local control and community self-determination in public health decisions.” He said he and fellow Republicans were weighing legal action. A lawyer for districts around Philadelphia said some school boards might consider ignoring the order.

With concern heightened by the approach of cooler weather and the inability to vaccinate children under 12, the decision reinforced how an event many hoped would restore a sense of normalcy — the return of all students to their classrooms — instead becomes a reminder the pandemic is far from over.

Masking is recommended for everyone in schools by the CDC, but Pennsylvania is just the the 15th state to require it. Delaware and New Jersey imposed school mask mandates weeks ago; so did the Philadelphia School District.

Pennsylvania’s new order comes as many districts are already back in session and the rest are poised to start within days — at the same time the variant has sent infections increasing and Americans have failed to get vaccinated quickly enough to beat it.

Beam, the health secretary, said more than 5,000 Pennsylvania students had already tested positive for the virus in the first days of the school year and pointed to a 277% rise in cases among children 17 and under between mid-July and August.

She said mask-optional schools are already seeing consequences, including in four different districts where football games were canceled Friday. New cases among children in day care have also increased significantly.

» READ MORE: This was supposed to be the return-to-normal school year. It’s going to be anything but.

The mandate is not tied to any specific metrics, but Wolf said officials would reassess the need for it by the first week of October.

Under the order, masks aren’t required during sports practices and games, in gym class, while playing an instrument, or when eating and drinking. They also are not required for people with certain medical conditions or disabilities and children younger than 2.

Some districts have already spent months battling over the mask question, which has stirred heated conflict among parents and been the subject of online misinformation campaigns. How districts that haven’t required masks will respond wasn’t immediately clear.

The Penn-Delco School District had only recommended universal masking but said it would now require it when school begins next week. The Quakertown Community School District, where classes have already resumed, told parents that it would require masks starting next Tuesday and that its lawyer had said the district must comply. In the mask-optional Pennridge School District, meanwhile, a spokesperson declined to comment.

» READ MORE: Mask and vaccine mandates have broad support, polls show. But some Pa. Republicans are campaigning against them.

Research into the efficacy of masks in school settings remains limited, though masking has generally been shown to significantly reduce the transmission of the virus.

Lisa O’Mahony, the medical adviser for Delaware County and a pediatrician, said that she understands frustration among those who want the pandemic to be over but that it simply is not yet and masking will keep kids safer.

“We’re in a place right now where the pandemic is really for the unvaccinated, and unfortunately we don’t have vaccines available for the under-12 age group,” she said, “so I don’t know if there’s any alternative to universal masking.”

Rich Askey, who as president of the Pennsylvania State Education Association leads the state’s largest teachers’ union, said the issue wasn’t just whether or not to wear a mask: “It is a choice between keeping schools open for in-person learning or forcing far too many students to learn from the other side of a screen.”

A fight ahead?

The governor’s emergency powers to sustain a state disaster declaration were curtailed by voters in the May election, but Beam issued the mask policy under the state’s disease-control law, as she did with Pennsylvania’s previous school and statewide mask orders.

Some lawmakers were discussing the possibility of amending the disease-control act to curb the administration’s power, Sen. Ryan Aument (R., Lancaster) said in a statement, while Senate President Pro Tempore Jake Corman (R., Centre) asserted Beam did not have the authority to impose any mitigation measures.

He said Wolf and his health secretary had just weeks ago been “adamant” about such decisions being made at the local level. “It is completely disingenuous for him to flip-flop now when he didn’t like the choices school districts made,” Corman said.

Jeff Sultanik, a lawyer who represents districts in and beyond the Philadelphia region, said he anticipated “there’s going to be immediately some districts will want to challenge, or not follow,” the mask order.

Wolf dismissed questions about the possibility of a challenge. He said he believed the desire to “do the right thing” and pressure from parents would lead schools to follow the mandate, despite acknowledging many chose not to adopt mask policies on their own.

» READ MORE: Central Bucks parents sue after school board votes against mask mandate

Hailey Gerena, 25, of Chester, said she was relieved to hear Tuesday’s news. Her 2-year-old son, Kingston, attends a Delaware County day care where she was told only half the staff were vaccinated earlier this summer.

“The most vulnerable population is our children because we can’t vaccinate them,” she said.

Some parents opposed to masking have argued it should be a personal choice, citing lower rates of infection and death among children.

“Our children have one childhood,” Central Bucks parent Jayd McFerson told the school board last week, before it voted down a plan to require masking and other measures recommended by state and county officials.

Following the vote, a group of parents sued that district, contending that their children, who have special needs, have a higher risk of severe illness and need more protection from the virus. A lawyer for the parents said Tuesday that they will keep fighting the district unless it both follows the state mask mandate and adopts other mitigation strategies.

In Bucks County, where a number of school boards had declined to impose mask requirements, the county Health Department endorsed masking only after the urging of local hospitals. Medical centers have been seeing an influx of younger patients with respiratory viruses that struck this summer, which means children hospitalized with COVID-19 could find few beds available.

The number of children hospitalized, combined with the rising case counts in the area, means that not masking in schools would present a serious risk, said Jeffrey Jahre, head of academic affairs and infectious disease specialist at St. Luke’s Hospital and Health Network, one of the hospital systems to lobby Bucks County officials.

“The trend is not going in the right direction and there’s no reason to believe it’s going to change in the next two or three weeks,” Jahre said of the virus’ spread, “and [it] in fact will get worse.”

Staff writers Andrew Seidman and Jason Laughlin contributed to this article.