The Philadelphia School District has pushed back its reopening date for a third time.

Superintendent William R. Hite Jr. said Wednesday 9,000 prekindergarten through second-grade students won’t return on Feb. 22 as planned but will instead go back March 1 amid an ongoing building safety dispute between the district and its teachers’ union. Students had been scheduled to return Monday.

The news left him “deeply disappointed,” the superintendent said.

Hite maintains that schools are safe but said he will not bring children back to classrooms that aren’t ready for them. Teachers were due back Feb. 8 but, at the direction of Philadelphia Federation of Teachers president Jerry Jordan, refused to report to school buildings and have been working from home. City school buildings have been closed since March 2020.

“Children need to come to classrooms that are ready to receive them, classrooms that are set up,” Hite said at a news conference at Cayuga Elementary in North Philadelphia.

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Hite and the PFT are still awaiting a ruling from Peter Orris, a mediator and Chicago doctor and public health expert, on whether the district has met reopening conditions spelled out in a fall agreement between the union and school system. Orris has reviewed documents and called both sides together for a meeting, but it’s still not clear when his ruling might land.

The city has said teachers are not expected to return until Orris makes his determination, meaning the March 1 date is not firm. Hite said he was “optimistic” that the school system’s fourth attempt at reopening would be successful.

Rich Lazer, the city’s deputy mayor for labor, said the mediator’s work to date has yielded “very robust conversations” with the PFT and district.

Asked if the March 1 reopening date was realistic, Lazer said he believed it was.

“I’m hoping we could have a decision before then,” Lazer told City Council on Wednesday. “I know that both sides are working diligently to get there.”

What that looks like remains unclear. Hite again suggested that individual schools where there are concerns about COVID-19 preparedness could remain all-virtual while schools that are ready reopen March 1.

“If there are buildings that we need to be concerned about, we will take them offline,” the superintendent said. “We are committing to opening schools one at a time if we need to.”

Just one-third of eligible students, or about 9,000, have signed up to return March 1. Hite said he knows the district will need to rebuild trust with families, but “the only way we’re going to build that is to get individuals back into schools.”

The superintendent remains emphatic: Children need the opportunity to return to school buildings as soon as possible.

“We understand the urgency of getting our young people back,” Hite said, noting that the pandemic has devastated poor communities and communities of color. “Many of our students are struggling academically, and others are suffering feelings of isolation and depression.”

Later, Hite suggested that some “children are losing. Children are not being educated.” While Philadelphia students lacked direct instruction for weeks last spring, classes have been operating fully virtually without interruption since September.

» READ MORE: In public protest, thousands of Philly teachers pushed back against reopening schools

Ventilation remains an area of great concern for the PFT, but Susan E. Coffin, a Children’s Hospital of Philadelphia infectious disease specialist who joined Hite at the news conference, said she believed the time to open schools is now, and that the focus on airflow was overblown.

“It’s not the airflow that determines whether or not we’re going to be safe,” Coffin said. “It’s how we use our spaces and how we interact together.”

District officials also announced that a school worker vaccination program, developed in conjunction with CHOP, begins this week, with employees already working in schools — food service workers, cleaners, principals — eligible for inoculation first, along with prekindergarten through second-grade teachers. Vaccine clinics will be held at CHOP, at four district schools, one parochial school, and an independent school.

It remains unclear how many doses will be available.

Larisa Shambaugh, the district’s human resources chief, also said school staff and 20% of students will undergo rapid COVID-19 tests weekly when they return. If students’ parents do not consent to the exams, the children must remain in virtual classes.

City Council took up school reopening in a Wednesday committee session, questioning district, union, and medical experts on the city’s plan and the science behind it.

David Rubin, director of CHOP’s PolicyLab, acknowledged that Philadelphia’s reopening challenges are different than many other districts. Still, Rubin said, he’s confident that the district can reopen “quite safely,” if protocols around masking, social distancing, hand-washing, and exclusion of those with symptoms are in place.

“We were greatly encouraged by the evidence that even large districts like New York City had very infrequent transmission when they opened their schools in the fall using strong, multilayered safety protocols,” Rubin said.

Jordan, the PFT president, told Council that the union “has never, and will never, stand in the way of student progress or access to education,” but he said he does not “yet believe that the district has shown us that buildings are safe for reoccupancy.”