All Philadelphia School District buildings will open Aug. 31 for full-time, in-person instruction, five days a week, Superintendent William R. Hite Jr. said Friday — and all students and staff will be required to wear masks, regardless of vaccination status.

The school system is also exploring the legality of making vaccines mandatory for all staff, Hite said.

“After 18 months of disrupted learning due to COVID-19, we believe that safely welcoming students back into classrooms with caring educators is the best way to help our young people heal ... from all the social and emotional traumas they have been experiencing recently,” the superintendent said at a news conference at Benjamin Franklin High School.

Hite said the district will meet or exceed all Centers for Disease Control and Prevention and Philadelphia Department of Public Health recommendations for COVID-19 protocols. Philadelphia will maintain three feet of social distancing when possible, though at many schools, such spacing will not be possible.

Weekly COVID-19 tests will be required for staff, and students will be tested if they exhibit symptoms. Those in close contact with positive cases will be tested at least three times within the first seven days of exposure, and those who remain negative can stay in school without quarantining. Positive cases will be required to isolate for at least 10 days.

Athletes in “high risk” sports, such as football, and students who participate in performing arts extracurriculars such as band and choir will be tested weekly, unless they opt out with proof of vaccination. That option is not open to vaccinated staffers.

Hite said he has explored the idea of making vaccinations mandatory for staffers.

“We have not gone that route yet, on advice from counsel,” he said. “When we can mandate it, we will.”

Families not yet comfortable with their children returning to in-person instruction will have the option of sending their children to Philadelphia Virtual Academy, the district’s cyber school. PVA has run for almost a decade, open to children in grades 6 through 12, but Hite announced Friday the school will now accept children in grades K to 5, as well.

PVA students unenroll from their home schools, but remain district students. The school is staffed largely by teachers from the Chester County Intermediate Unit, the local education agency that runs virtual schools for a number of area districts.

The enrollment window for fully virtual school opens Monday and lasts two weeks.

It’s not yet clear how many families will take advantage of the PVA option, but Hite said that even if large numbers of students sign up, in-person schools won’t lose teachers because of a commitment to end “leveling” — the process of shifting teachers from school to school based on student enrollment — for this year.

Alisa Shields, a parent whose daughter will enter first grade at E.M. Stanton in the fall, can’t wait to send her daughter back to in-person school, she said.

“It’s really important for her to be around her peers,” Shields said at the news conference. “Being at home was hard for her, and I could see her attitude change” with online kindergarten, despite a skilled teacher. “She was disinterested in everything.”

The girl brightened when she went back to school two days a week in the spring.

“We are just so excited about the opportunity to return to school five days a week,” Shields said.

When some students returned to class part-time last spring, the district and Philadelphia Federation of Teachers performed air balancing tests and cleared classrooms for occupancy, limiting the number of students in each room based on ventilation conditions. Hite said that with the addition of air purifiers in every classroom, those limits will be lifted and rooms won’t need to be cleared.

“If, in fact, we have the purification devices in instructional spaces, then there’s no need to do the assessments,” Hite said.

The district spent $4.5 million on the air purifiers, though questions have since arisen about the devices, which experts say are ineffective at reducing the spread of coronavirus and could potentially create harmful chemicals.

» READ MORE: Philly schools are spending $4.5 million on air purifiers to curb COVID-19. They won’t help much, experts say.

Top district officials met with Michael Waring, professor of indoor air quality and department head of civil, architectural, and environmental engineering at Drexel University, who initially raised concern over the air purifiers.

Hite said the purifiers are a lock, but he takes Waring’s recommendations seriously and is consulting with his own experts about Waring’s concerns.

“If in fact we need additional purification devices in spaces, we would add additional purification devices,” Hite said.

Hite and Chief of Schools Evelyn Nuñez said the district was proceeding with changes to schools’ start and end times, a controversial move they said was necessary to standardize bus routes, especially amid a shortage of transportation workers.

» READ MORE: Philly wants to change some schools’ schedules by as much as 2 hours. People are up in arms.

The changes would shift some high schoolers’ start times considerably earlier, contrary to what research shows is beneficial for adolescents.

Hite and Nuñez said they worked collaboratively with school communities, but many teachers and parents feel blindsided with the changes, which could clash with parents’ work schedules and some families’ need to have older siblings get younger ones to school.

“We will continue to have forums with our stakeholders as we think about the ‘22-’23 school year,” said Nuñez.

Shifts to schools’ bell schedules have drawn fire from some public officials, including Councilmember Helen Gym.

“Time and again, the district falls short of a basic responsibility: seeking public input before decisions happen, not after,” Gym said in a statement. “We must go back to the drawing board to develop schedules that are in the best interest of our students and our city.”

Another question mark hanging over the year is the teachers’ contract. The PFT’s one-year pact with the district expires at the end of August, as does the contract with the district’s principals’ union.

Negotiations are happening regularly, Hite said, and he remains confident that a PFT deal will be struck by the first day of school. The union for years lacked the power to strike, under state takeover law, but with the school system back under local control, a strike is back on the table.

“We’ll remain in active negotiations until we resolve the contract,” said Hite. “We hope that it will be resolved by that time.”