Philadelphia students and teachers will not return to school buildings Monday, but a decision is close on when some of them might be able to do so.

Hours after saying he remained “optimistic” that a partial reopening could begin next week as had been planned, Superintendent William R. Hite Jr. told the school board Thursday evening that the district, the Philadelphia Federation of Teachers, and city officials are still in negotiations with a third-party mediator on when and how to reopen.

Hite said they will announce on Monday when prekindergarten through second-grade students are eligible to come back to buildings. For now, all 120,000 city students “will remain virtual until further details are announced,” Hite told the board.

Monday was to be the day about 9,000 prekindergarten through second-grade students — kids whose families opted for them to return to school buildings two days a week — had been scheduled to return. It would have been the first time in nearly a year that Philadelphia public school students got in-school instruction.

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Monday’s scuttled reopening represents the fourth try for the district, which previously attempted to send children back into buildings in September, November, and February. Rising case counts and pushback from parents and teachers quashed those plans.

Philadelphia students have been out of school for nearly a year; children in the 120,000-student system last attended school in person on March 13.The district and the teachers’ union have been in negotiations with Peter Orris, a Chicago-based doctor, for two weeks. The Philadelphia Federation of Teachers had previously refused to send its members into buildings it deemed unsafe.

Orris has not made a decision but has held multiple meetings with both sides. Mayor Jim Kenney has been involved in the negotiations, according to people familiar with the talks.

Kenney, in a statement Thursday night, said he appreciated “the good faith effort” shown by both sides.

“We are excited to be nearing the end of the process and look forward to providing our Philadelphia community with more certainty about the reopening of our public schools, starting first with our youngest learners,” Kenney said.

Hite, in an email to staff obtained by The Inquirer, told teachers he knows the uncertainty around reopening has been “unsettling for many staff members, students and families” but said, “There are still some important details that are being worked out, and we want to have those details finalized so we can announce the full phase-in plan for PreK-2 hybrid learning students at one time.”

Both Hite and PFT leader Jerry Jordan indicated Thursday that when an agreement is reached, it will be to open only some of the buildings.

Jordan, in an email sent to his members, said the district recently released about 1,000 pages of new information about building readiness, which union staffers are scrutinizing. Jordan vowed to protect members’ safety and said, “This will likely include keeping certain buildings closed while others open.”

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Concerns have centered on ventilation in the district’s aging buildings. In schools that lack mechanical ventilation, window fans have been installed as a solution to promote airflow, a fix the union has denounced as decidedly inadequate.

Some teachers have balked at the idea of limiting the reopening to just some school buildings, which they say raises equity issues.

Hite, in a Thursday interview with Radio Times, said he was not “under-appreciating the good work that teachers have been doing in classrooms since this pandemic started. They’ve been doing extraordinary work.”

But, he said, if teachers are expected back to work and choose not to return, there will be consequences.

Achieving a reopening through mediation is the goal, Hite said, but “we may have to default, at the end of the day, to just requiring individuals back, and then we would have to take the necessary steps if individuals decide not to come back.”

Reopening drew passionate testimony from both those wary of sending students back now and those who say they have been out for too long.

Children have been out of Philadelphia school buildings for 344 days, noted Michael Gorman, a district parent, and suburban and private-school students are largely back in classrooms.

“Only the [Philadelphia School District] kids are trapped behind the screen,” Gorman said. “Learning loss is staggering. And the mental health issues are heartbreaking.”

Still, many parents are not ready to send children back. Two-thirds of those families eligible to send children back when buildings reopen are opting to keep them at home.

And Sarah Kloss, a parent at Jackson Elementary, said a parent organization at that relatively affluent school has been asked to raise funds for basic safety supplies. The school does not have enough desk shields for all children. Jackson has resources to help, but what about other schools? Kloss asked.

“The schools with higher percentage of Black and brown students ... are simply told to do without,” Kloss said.