New York City Mayor Bill de Blasio has delayed the reopening of schools for in-person learning until Sept. 21.

Before the announcement by de Blasio, New York City schools were set to reopen for in-classroom learning on Sept. 10. Now students will begin classes remotely on Sept. 16, with classrooms reopening the following week for students in what de Blasio called a blended model in a news briefing streamed by WABC, an ABC affiliate out of New York.

“So it’s blended learning, some kids in school one day, other kids in school another day,” he said. “The buildings will be open and operational and taking kids in for that crucial in-person learning.”

The decision by de Blasio came after he said he reached an agreement with the teacher’s unions – the United Federation of Teachers and Council of School Supervisors & Administrators. The United Federation of Teachers had previously threatened to strike if teachers returned to school without proper safety precautions in place during the coronavirus pandemic.

Safety measures called for at the time included personal protective gear, cleaning supplies, enhanced ventilation, and a virus testing program for staff and students. A randomized testing program was agreed to by de Blasio and the teacher’s union as part of the agreement to return to school.

With the delay in reopening schools, teachers and administrative staff will be allowed more time to ensure buildings are safe for students, de Blasio said. Teachers will return to school on Sept. 8, as previously scheduled.

“There is nothing more precious than taking care of the children of New York City,” de Blasio told reporters Tuesday during a news briefing. “It’s a very complex moment in history, to say the least. Real powerful issues had to be discussed, and resolution had to be found.”

President of the United Federation of Teachers in New York City said the agreement with de Blasio was an example of “how to get things done.” He continued by saying that New York City schools will hold the most “aggressive policies and greatest safeguards.”

New York City has reported over 230,000 positive cases of the coronavirus with over 19,000 COVID-19 deaths, according to data from NYC Health.