Classrooms opened for about 1 million New York City public school students Monday in the nation’s largest experiment of in-person learning during the coronavirus pandemic.

The start of the school year happened the same day the city took several big steps toward recovery from the pandemic.

Nearly all of the city’s 300,000 employees were required to be at work in person Monday. Most will need to be vaccinated or undergo weekly coronavirus testing to remain in their jobs.

The city was also set to start enforcing rules requiring workers and customers to be vaccinated to go indoors at restaurants, museums, gyms and entertainment venues. The vaccination requirement has been in place for weeks but had not been enforced.

There will also be a vaccine requirement — with no test-out option — for teachers, though they have been given until September 27 to get their first shot.

Unlike some school districts that are offering online learning to families that prefer it, New York City officials say there will be no remote option despite the persistence of the highly transmissible delta variant of the coronavirus.

New York City kept schools open for most of the last school year, with some students doing a mix of remote and in-person instruction, but the majority of families chose all-remote learning. That choice won’t be available this year, Mayor Bill de Blasio has insisted.

“Our kids need to be in school, and it’s unbelievable that some kids haven’t seen the inside of a classroom for a year and a half,” the mayor said Thursday. “There are massive consequences to that, including health care consequences. The healthiest, best place for kids to be is in school.”

Masks will be required for all students and staff members, as is the case in schools across New York state.

There is no requirement for students 12 and older to be vaccinated, but vaccinations will be required to participate in contact sports such as football and basketball as well as some extracurricular activities such as band and theater. About two-thirds of the city’s 12-to-17-year-olds are vaccinated.

In the United States, anyone 12 and older is eligible to receive a coronavirus vaccine. The Food and Drug Administration’s vaccine chief said last week that he is hopeful children as young as 5 will be eligible to get vaccinated by the end of 2021.

— Associated Press