Philadelphia’s school and city leaders on Wednesday announced plans to reopen schools in September, but not fully, with most children attending in-person classes two days a week.

Ending weeks of buildup, the district said it would open two days later than planned, with more staff, less crowded classrooms, and promises to scrub and sanitize buildings to minimize the spread of the coronavirus in the school system of 125,000.

Superintendent William R. Hite Jr. said the extra steps would come at a cost — possibly $80 million or more — and cautioned that public health conditions could shift abruptly and force a return to 100% remote instruction.

Philadelphia Health Commissioner Thomas Farley acknowledged that a return to in-person school carries risks.

But, Farley said at a news conference, “for their long-term success, including their long-term health, children need to learn. As a society, we need to find a way to balance those risks.”

The plan comes four months after COVID-19 abruptly shut schools and sent students home for an extended, unexpected break; Philadelphia students went six weeks without learning new material, and the shutdown exposed significant educational gaps in the high-poverty district, with thousands of students unable to access learning materials.

It faced immediate pushback from some staffers, who fear the Philadelphia School District’s guidelines do not sufficiently safeguard them from COVID-19 infection. The plan also raised questions about whether the district can adequately clean its buildings, many of which have often had shortages of toilet paper, soap and hot water; keep secondary students, who rely on public transportation, safe; accommodate staff with health concerns in a workforce where 72% of teachers are 50 or older; persuade students to keep their masks on; and get thousands of children without internet access online.

Hite, who said the district would need an infusion of federal funds to pay for the plan, urged parents, staff, and students to brace for a new normal.

“We all want to return to school in the way that we have been most accustomed to, but COVID-19 has taught us that we must be willing to adopt practices that might not be what we are used to, but practices that will be absolutely required to stop the spread of this virus,” the superintendent said.

Hite will seek to move the first day of school to Sept. 2, instead of Aug. 31 as planned. The shift will allow for an extra week of training to prepare staff for teaching and provide student supports during the pandemic. He said the school system would need to hire more workers, including teachers, but could not say how many until it becomes clear how many parents will choose the 100% virtual option the district is offering.

Each of the district’s 200-plus schools will develop its own operations plan to execute the guidelines, including: social distancing, masks or face shields for all staff and students, a ban on nonessential visitors, and meals eaten mostly in classrooms. In addition to sanitizing classrooms, the school system pledged to have adequate supplies and ventilation inside its buildings, but said it would not conduct temperature checks. Students and staff would screen themselves for health problems.

Classroom capacity will be limited to 25 people “when feasible,” according to the plan; officials said they hoped most classes would have 12 to 15 students. When children cannot be six feet apart, plastic glass barriers will be “prioritized.” Student desks should face forward, the district said — though at many schools, students now sit in groups at tables.

English, math, art, music, and physical education will be given priority for face-to-face learning, the district said, meaning such subjects as social studies and foreign language could be fully remote. The district also said career and technical education classes may become in-person.

Preschoolers and students with complex needs will attend school four days a week. Athletics and extracurricular activities will resume eventually, with a phased-in approach to getting students back on sports fields and possible changes to contact sports.

Attendance will be taken, and students will be graded, a shift from the policy suspension last spring that said students could receive final grades no lower than what they had earned on March 13, when the coronavirus shut down classes.

Students and staff who test positive for COVID-19 are expected to remain out of school for at least 10 days and until symptom-free, but will not need to show a doctor’s note or a negative COVID test upon return.

Officials said they would launch a program to cope with the trauma and stress students have experienced because of the pandemic.

The next seven weeks will be a sprint to ready buildings for a school year unlike any other and develop systems to support teaching and learning. Philadelphia Federation of Teachers president Jerry Jordan said he had “a number of concerns” that must be resolved. The teachers’ union did not sign off on the plan, Jordan emphasized.

Particularly concerning are the existing ventilation issues at many schools, Jordan said; Hite said some sections of schools that have typically been used may be uninhabitable. Jordan also worries about the district’s ability to keep schools stocked with basic health and sanitation supplies given the pandemic and the district’s past inability to keep schools stocked.

“You can’t have people responsible for running the buildings if you don’t give them the tools they need,” said Jordan.

Zoe Rooney, who teaches at Strawberry Mansion High, felt the plan was short on details.

“I don’t see enough that addresses classroom-based safety,” said Rooney. “Even if we split my classes in half, looking at the size of my classroom, that’s still too many kids to sufficiently distance.”

Rooney, also the parent of two children in district schools, said she’s glad the district is planning to return children with complex special needs to school four days a week. But she and others will still be left with real child-care concerns — some of her friends have told Rooney they may need to quit jobs to make just two in-person days work.

“There are so many burdens on families,” she said.

Robin Cooper, president of the district’s principals’ union, said she understands the district is in a tough spot, but she believes a better course of action would be to start the year virtually until more is known about the virus. And she wondered why news conferences and school board meetings are being held remotely, but teachers and students are being sent back into spaces where social distancing won’t always be possible.

“I’m worried that we haven’t conquered the virus enough to say, ‘Open schools,’ ” Cooper said. “I’m worried that we’re trying to avoid an economic collapse, but I just don’t think putting our most vulnerable back to school is the way we show that we’re moving ahead.”