Reversing course, Mayor Eric Adams is now celebrating and supporting a state law that is forcing New York City schools to reduce class size.

It’s a mandate that’s been on the books since 2022, but city officials — including Adams — have criticized it because it’s been estimated to cost the city billions of dollars.

“It’s the best way to help our students learn,” Adams said on Wednesday during a press conference at P.S. 88 in Ridgewood, Queens.

“Walking in here, you are making them feel as though everything is possible, and the possibility lies on being able to have the close interaction and relationship. And nothing really personifies that more than smaller class sizes,” he added.

Adams is changing his tune, after previously complaining that lower-class sizes could hurt other programs like special education, summer school and dyslexia screenings.

Now the mayor promised the city will hire at least 3,700 teachers by September. But parents have questions.

Deborah Alexander backs smaller class sizes, but thinks the city Department of Education should not reduce classes all at once.

“We don’t have an unlimited pit of money, we don’t have unlimited space, and we don’t have unlimited teachers. So something has to give,” Alexander told NY1.

“We’re not getting a number of teachers who are retiring or general attrition for teachers for next year. Are these teachers that we’re supposedly hiring to alleviate class size — going to just fill vacancies?” she said.

Starting salaries for teachers without a master’s degree will soon be almost $69,000.

City Hall won’t say how much the new hires will cost the city.

It’s also unclear whether schools can physically fit students in current buildings, despite assurances.

“We’re not gonna tell a parent who lives across the street from a school: you can’t go to that school,” Michael Mulgrew, president of the United Federation of Teachers, said.

The union heavily lobbied the legislature to pass the measure and stands to benefit if thousands of more teachers — dues paying union members — are hired.

In 2022, Gov. Kathy Hochul signed a law requiring the city to cut public school headcount.

“There’s a reason why we had to pass this legislation, to ensure that kids are not remaining in overcrowded class sizes — in class sizes that are far larger than the rest of the state,” Queens Democratic state Sen. John Liu, the original bill sponsor, said.

According to the law, by the 2027-2028 school year, kindergarten through third grade classes will be capped at 20 students; 23 students for grades fourth through eight; and 25 students for high school.

All in, City Hall may spend $2 billion annually, according to previous reports.

Then, there’s always the political side to the story.

Adams is running for re-election this year and he’s badly wounded. Although his federal criminal corruption case was dismissed, he’s shed loyalists and is now running as an independent.

“Whatever the reason may have for finally doing this, I’m glad it’s being done. But that’s not all. There needs to be more efforts to continue to be in compliance over the next couple of years,” Liu offered.

Also complicating the issue: there’s already a natural lowering of class sizes thanks to declining enrollment.

Currently standing at just over 900,000 — a roughly 100,000 student decline compared to the 2019 school year.