After four false starts and with a mix of both relief and caution, Philadelphia city, school, and teachers’ union officials on Monday announced a deal to begin bringing students and staff back to classrooms for the first time in nearly a year.

Some teachers will begin reporting to their buildings on Wednesday. Students at 53 schools citywide will start in-person classes on Monday. The return will then continue in waves, with a group of about 50 schools every week reopening, first for prekindergarten through second-grade students, through March 22.

Though just a fraction of the district’s 120,000 traditional public school students is eligible to return Monday, eventually all children will be invited back, officials said.

“We all agree that the time is right to get our young people back into school buildings,” Mayor Jim Kenney said at a news conference at Richard Wright Elementary School in North Philadelphia, where he joined Superintendent William R. Hite Jr. and teachers’ union leaders.

“There is a will — teachers, food service workers, they understand that in-school learning is better. They want to be safe, as do the parents of our kids,” said Randi Weingarten, the national teachers’ union president, adding that without compromise, “this could have gone really badly for a very long time.”

A reopening plan for months had been stalled by safety concerns, exacerbated by what had been the winter surge in coronavirus cases, the slow rollout of the vaccine, and the School District’s long history of environmental problems in some buildings.

Philadelphia Federation of Teachers president Jerry Jordan had directed his members not to report to schools. Instead, many worked from outside their buildings, teaching from tents and joining supporters to stake out their skepticism on the district’s pledges that schools are safe. And only last week did Philadelphia’s teachers as a group begin getting their shots.

But this fifth bid to reopen — attempts were previously made to bring students back in September, November, and last month — is likely to stick, given the union’s buy-in.

Every city classroom that will be reoccupied has been vetted by the PFT’s environmental scientist, the union said. The School District’s widely ridiculed proposal to use window fans to ventilate some classrooms was abandoned; instead, air purifiers will be purchased for rooms that lack adequate ventilation.

Students and teachers will be spaced at least six feet apart and required to wear masks. Students will prescreen at home; 20% of children in schools will be COVID-19 tested weekly; staff will also be tested weekly.

Peter Orris, a Chicago doctor and occupational health expert appointed as a third-party mediator, worked with both sides since early February to get a deal done. The intervention of Kenney and of Weingarten was also key, according to people with knowledge of the talks.

For months, Jordan had said he was not comfortable with teachers returning to buildings without information to guarantee his members’ safety. It wasn’t until mediation began that the union got more than 1,000 pages of records — specific, school- and room-level data — to convince the PFT that buildings could be reoccupied.

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Hite maintained, as he has for the past month, that all schools are safe for student and teacher occupancy. But, he said, “I’m not the king. Me declaring all schools are safe doesn’t make everybody else feel like that, so I want to make sure we have a process to work through.”

Questions still loom, including how many students will show up next week. When all prekindergarten through second graders were eligible to return, just one-third opted to come back, and their parents made those choices in the fall.

Also unclear is whether all teachers will return. Some have questioned a staggered return that deems some schools safe but says others are not yet ready.

Steinberg, who leads the American Federation of Teachers Pennsylvania and Philadelphia’s health and welfare fund, said educators had been fighting for students’ safety.

“They taught outside on the coldest day of the year, in 19-degree cold, to demonstrate just how serious they are about their profession and about the work that they do serving our young people each day,” Steinberg said at the news conference. “That work continues each day whether they are teaching in person or remotely.”

Though the union and district put up a united front, Steinberg called the past weeks “enormously challenging” and said “the level of trust is not great” yet. Steinberg also said he wants children back in school as quickly as is possible, but said no school will open unless it’s ready.

“I wish that we could stand up here today and announce that every single building is safe for reoccupancy, but we’re not quite there yet,” he said.

The fragile peace bridging the teachers’ union and the district will be tested quickly, as both sides must still hammer out reopening for the next groups of schools, as well as students beyond second grade. Hite said he wants to move “as quickly as we possibly can” to bring back all students.

Kate Sannicks-Lerner, a kindergarten teacher at Julia deBurgos Elementary in the Fairhill section of North Philadelphia, a school cleared to welcome students next week, initially said she would not return to her classroom. But Sannicks-Lerner is preparing to go back, slightly more confident because she’s receiving her first COVID-19 vaccine Friday and because she feels the district and union have scrutinized specifics about each room at her school.

“I’m feeling excited, but I’m also anxious — what are small groups going to look like? How is it going to work for my special-needs kids, some in the classroom, some at home? I can’t even imagine how we’re going to do this,” said Sannicks-Lerner.

Jessica Lewis is nervous about going back to teach kindergarten at Juniata Park Academy on Wednesday but also delighted.

“I really miss seeing them every day in person,” said Lewis. “I know we can’t hug them, but I’m going to give them air hugs from six feet away.”

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Shakeda Gaines, who leads the city’s Home and School Council, said the majority of the hundreds of parents her group surveyed reported they were not comfortable sending their children back to school in a pandemic.

“This is about parents and children feeling safe,” Gaines said. “We’re still dealing with asbestos, mold, and lead in schools — that hasn’t gone away. A lot of people are still scared.”

But some parents were like Amy Blumenthal, whose son attends Greenfield Elementary, a school in Center City chosen for the first wave of reopening. Blumenthal said she’s spent sleepless nights worrying about her son, a kindergartner, missing out on his first real school experience, and that Monday’s news was a revelation.

“I had tears in my eyes when I found out we were reopening,” Blumenthal said. “To me, this is the light at the end of the tunnel.”