The announcement marks a major policy reversal for the nation's largest school system, less than two weeks after de Blasio, a Democrat, announced that schools were shutting down because of a rising number of COVID-19 cases in the city.
New York City's District 75 schools, which serve students with special needs, will reopen for all grade levels on Dec. 10.
"One of the things that's been very clear is folks wanted school to keep moving forward and be open so long as it could be done safely," de Blasio said at a press conference on Sunday. "One of the crucial things we heard from our union partners is more testing and required consent forms or medical exemptions."
"A lot of people have been saying, rightfully, a lot of parents, we've heard your voices loud and clear: you wanted schools back open, but we're going to ask everyone to be a part of that, everyone to participate to make it work," he said.
De Blasio added on Twitter that "wherever possible we will move to 5 day a week in-person learning."
"We want our kids in the classroom for as much time as possible," de Blasio wrote. "Our families do, too. We’ll work to make it happen."
Earlier in November, protesters gathered outside City Hall in Manhattan to criticize the mayor for shutting down the nation’s largest public school system due to spiking coronavirus infections, even as Catholic and other elite private schools in the city are allowed to remain open for in-person instruction.
Meanwhile, CDC Director Robert Redfield has said that school is among the "safest" places for children to be.
“The truth is, for kids K-12, one of the safest places they can be, from our perspective, is to remain in school, and it’s really important that following the data, making sure we don’t make emotional decisions about what to close and what not to close,” Redfield said earlier in November. “I’m here to say clearly the data strongly supports that K-12 schools — as well as institutes of higher learning — really are not where we’re having our challenges.”
In October, the CDC updated its report on COVID-19 Trends Among School-Aged Children — United States, which analyzed health data between March and September.
Research at the time showed out of 277,285 positive coronavirus cases in schools throughout the country, transmission among adolescents between the ages of 5 and 11 was approximately half that among children between the ages of 12 and 17.
Fox News' Hollie McKay, Danielle Wallace and Cortney Moore and the Associated Press contributed to this report.