“It’s a new approach because we have so much proof now of how safe schools can be, and this has come from real life experience of the biggest school system in America,” de Blasio said when asked about his decision to change the threshold for school closures once again. “We feel confident that we can keep schools safe.”

The mayor laid out the reopening plan during a press conference Sunday, less than two weeks after he shut schools as part of a deal he had struck with the teacher’s union to close the buildings when the citywide transmission rate hit a weekly average of 3 percent. Sunday’s seven-day, citywide positivity rate was 3.9 percent.

The city will no longer use the 3 percent cutoff to determine school closures instead relying on specific Covid-19 cases at each school.

“I feel for all our parents who are experiencing so many challenges right now — how important it is to have their younger kids in school,” de Blasio said. “We now believe we know what we didn’t know back in the summer — we know what works through actual experience.”

Families will have to give consent for students to be tested once a week. Those who don't will not be allowed to attend in-person classes, de Blasio said. Only students who opted for in-person learning earlier this year will be able to attend, but they will now have classroom instruction for five days a week, rather than the blended model the city used before.

United Federation of Teachers president Michael Mulgrew, who has held significant sway over City Hall’s actions during the course of the pandemic, said he supported the policy as long as "stringent testing is in place."

"This strategy — properly implemented — will allow us to offer safe in-person instruction to the maximum number of students until we beat the pandemic," Mulgrew said in a statement.

De Blasio’s decision to shut schools two weeks ago sparked anger within City Hall, with most public health and high-ranking administration officials advising against it, according to four people involved in the talks. They felt he was gratuitously kowtowing to Mulgrew, who ended up admonishing the system that affords mayors control over public schools just days after he signed off on the closure plan.

“Closing schools was deeply frustrating after all the work that went into opening them and how much a success it had been,” said one administration official, who would only speak on the condition of anonymity to discuss internal deliberations.

The official, who is involved in the city’s pandemic response, said the decision to close schools was “based on a conservative approach that was out-dated after all the data [was] collected. The fact that we couldn’t pivot sooner was disappointing, but now we’re in the right place.”

The news will likely be a relief to parents of younger students who have criticized the mayor's decision to close schools while restaurants, bars and gyms have remained open in a limited capacity. Gov. Andrew Cuomo has ultimate authority over those businesses and has said they will have to face renewed restrictions.

Cuomo told reporters Sunday he believes the plan is “the right decision,” given the facts and information public health officials now have about Covid-19 infection rates among younger school children.

“Keeping schools open, where safe, is best,” he said during an afternoon conference call. “And I think New York City opening schools is the right direction and the right decision.”

How to manage the city’s network of public schools has arguably been the biggest challenge de Blasio has faced during the pandemic. He agonized over whether to shut them during the virus’s surge in March, initially holding off — despite advice from the city’s health department — out of concern for delayed academic progress and working parents who cannot afford private child care. Days later he closed schools for the remainder of the academic year and, after several more delays, announced a blend of in-person and remote learning.

About half of the city’s 1.1 million students had opted to attend some in-person classes, though just about 283,000 showed up through October, according to city data.

Asked about his original call to shutter schools, the mayor replied, “I felt bad about it for sure and I didn’t want to do it, but I felt we had to keep the commitment we made.”

The latest blueprint, he added, “is what’s going to take us through until we have a vaccine.”

Shannon Young contributed to this report.