New York City is shuttering schools to try to stop the renewed spread of the coronavirus, Mayor Bill de Blasio said Wednesday in a painful about-face for one of the first big U.S. school systems to bring students back to classrooms this fall.

The nation's largest public school system will halt in-person learning Thursday, the mayor and schools chancellor said. During a press conference, he said remote learning will continue through at least the Thanksgiving holiday.

The city had said since summer that school buildings would close if 3% of all the coronavirus tests performed citywide over a seven-day period came back positive. As the rate neared that point las week, de Blasio advised parents to prepare for a possible shutdown within days.

The mayor said the rate has now passed that mark.

"We are in the midst of a challenge and we can't let this deepen," says de Blasio. "We have held off the second wave and there is still more work to be done. We are going to need everyone to get tested and pay attention."

Some parents say the move is backwards, but expected. They say it's been a long few months with a lot of back and forth.

UFT President Michael Mulgrew issued a statement saying, "The city established the 3% infection rate threshold to make sure that schools did not become centers to spread the coronavirus. Since the 3% rate has been reached, education will continue but all students will be learning remotely. Now it's the job of all New Yorkers to maintain social distance, wear masks and take all other steps to substantially lower the infection rate so school buildings can re-open for in-person instruction."

Department of Education officials say community-based early childhood and family care programs, as well as Learning Bridges sites, will remain open to serve children and families in person.

"It is important that we follow the advice of our medical professionals so we are able to get back to in-person learning as quickly as possible," says NYC Schools Chancellor Richard Carranza. "That's how we will get our schools back open to in-person learning "

The city's more than 1 million public school students will now be taught entirely online, as most already are. As of the end of October, only about 25% of students had gone to class in school this fall, far fewer than officials had expected.

Parents, teachers and officials say the rate of transmission is low in schools compared to the city wide average. Over the past month, the city reported 2,306 cases among students and staff compared to the past seven days in the city where there were 7,790 cases.

To keep students spread out, the city offered in-person learning only part-time, with youngsters logging on from home the rest of the time.

The reopening date, originally set for Sept. 10, was postponed twice as teachers, principals and some parents said safety precautions and staffing were inadequate, with the teachers' union at one point threatening to strike.

The city agreed to changes, including hiring thousands more teachers and testing 10% to 20% of all students and staffers per month for the virus.

When high schools finally opened their doors, de Blasio hailed it as “an absolutely amazing moment” in the city's recovery.

“This is an example of what makes New York City great,” he said at the time. “We did something that other cities around this country could only dream of because we have fought back this pandemic so well for so long.”