It’s time to go sit in the corner, Billy!

Mayor de Blasio finally admitted Tuesday that his costly and controversial Renewal plan to fix nearly 100 of the city’s worst schools was a failure — pulling the plug on a years-long effort that cost taxpayers $773 million.

“We did not say everything would be perfect,” the mayor said, offering a huge understatement to describe a program that saw one-quarter of its schools either closed or merged.

“We said we were ready to go out there and create real investment, help kids right now, and see how many schools could really turn around.”

In reality, according to the Education Department, less than one-quarter of the schools in the Renewal program improved enough to exit after three years.

The move came nearly two years after The Post published an award-winning series of stories that exposed plunging enrollment, a surge in per-student spending and widespread failures to meet improvement goals at ­Renewal schools.

The “Education Boondoggle” series also revealed that scores of “leadership coaches” were hired for as much as $1,400 a day, including a retired principal who lied to corruption investigators, and the co-author of a book written by then-Schools Chancellor Carmen Fariña.

CUNY education Professor David Bloomfield on Tuesday accused de Blasio of using the Renewal plan as a ploy to “differentiate himself” from his predecessor, Mike Bloomberg, who had a policy of closing failing schools and then breaking them up into smaller “academies” with new administrations.

“This was done more for political reasons than for clear instructional benefit. There needed to be a scalpel here, not a hammer,” he said.

“But I do give the mayor props for admitting defeat.”

When de Blasio announced his School Renewal Program in November 2013, he pledged it would turn around 94 poorly performing schools with infusions of taxpayer cash to fund an extra hour of daily instruction, special training for the teachers and social services for the students.

Since then, the DOE has closed 14 of the schools and merged nine others for failing to make the grade.

In a 16-page, postmortem on the Renewal program, the DOE blamed its demise in part on a bureaucratic “organizational structure that sometimes left principals confused about lines of authority and sources of guidance, including an overly ‘one-size-fits-all’ approach.”

The report also faulted the principals themselves, saying it was a “formidable challenge” to find administrators with the necessary “talents and qualities.”

The DOE even blamed parents for shunning Renewal schools out of fear “that those schools were ‘bad’ and would soon be slated for closure.”

But the bulk of the report focuses on the “lessons learned” from what it describes as “by far the largest school turnaround effort pursued in any U.S. city.”

“Closely examining the commonalities in the Renewal schools that most significantly improved, as well as problems that arose in Renewal schools that made slower or insufficient progress, will raise the probability of success going forward,” it says.

The report was first obtained by The New York Times, to whom de Blasio also bluntly confessed his mistakes with the Renewal program.

“I would not do it that way again,” he told the paper.

During an unrelated news conference in Elmhurst, Queens, de Blasio on Tuesday claimed “45,000 students benefited from the Renewal initiative,” saying that “the money that was spent was helping students in real time to have better outcomes.”

“It went to summer programs, tutoring programs, mental-health clinics that were available to kids in those schools, all sorts of things that we would like to see in more and more schools,” he said.

“And a lot of kids benefited, which is why you see across all 94 schools in total a lot of progress that was achieved in terms of increased graduation rates, better test scores, better attendance.”

The mayor — who has been flirting with a presidential run and spent the past weekend in Iowa — also compared himself to one of his political heroes, President Franklin Delano Roosevelt.

“The New Deal transformed this country, many elements of which are with us to this day, like Social Security,” de Blasio said.

“We remember Social Security because it’s with us to this day. We do not remember some of the initiatives that they tried and did not work.”

“They learned in the Roosevelt administration, you know, by trial and error in many cases, but they had a very clear understanding: Be bold, be aggressive, be creative,” he added.

Schools Chancellor Richard Carranza also called the Renewal plan an “absolutely appropriate” attempt to address problems “that no one has solved at 100 percent.”

Leonie Haimson, founder of the Class Size Matters advocacy group, said, “I feel like I’m watching the same movie for the 1,000th time,” and added that de Blasio’s “approach is just to continue with the same BS.”

“Unless you address these out-of-control class sizes, nothing is going to change,” she said.

“You can’t just put the blame on principals or bureaucracy and structure.”