The city’s school system gets little bang for its buck.

While per-pupil spending has skyrocketed, student performance has hardly budged — and in some areas has slid — according to standardized measurements.

The city Department of Education, which serves nearly 1 million kids and controls a $23.4 billion budget, now spends an average $25,087 per student, up 40 percent from $17,928 in 2008-09, records show.

An Independent Budget Office analysis of 2015-16 operating expenses found a whopping chunk of that money — 30.3 percent — went for fringe and pension benefits for DOE employees and retirees.

The next biggest piece — 23.4 percent — went for teacher salaries, which the de Blasio administration raised in 2014 in a union contract that also cut instructional time for students.

New York City spent the most per pupil of any of the nation’s 100 largest school systems in fiscal year 2015, the US Census reported last week.

“It’s sad that we lead the nation in school spending with some of the lowest results,” said Sam Pirozzolo, a Staten Island father of two and vice president of the watchdog NYC Parents Union.

He marveled at the price tag: “How can it be possible in a system that spends $25,000 per student that schools require parents to send in tissues, notebooks, pencils and other classroom supplies?”

One main reason: The city is shoveling more and more dough into its Teachers’ Retirement System, a pension fund that, by state law, guarantees a 7 percent annual return — no matter what its investments do.

“When it comes to teacher retirement costs, the city is just pouring more money into a leaky bucket,” said E.J. McMahon, founder of the Empire Center for Public Policy think tank. “It has nothing to do with pupil performance.”

In expenses last year, 2,215 retired educators received annual payments exceeding $100,000, up from 1,595 in 2013 and 766 in 2008, records analyzed by the Empire Center show.

Another reason for rising costs, experts charge: Hundreds of millions of taxpayer dollars are squandered.

City Comptroller Scott Stringer recently blasted the DOE for “a lack of transparency and detail that is frightening when you are talking about billions of dollars earmarked for our children.”

Last month, for instance, Stringer said his office found that the DOE paid $350 million to boost broadband Internet access in schools — while few faculty and administrators were satisfied with the service.

In addition, auditors found virtually no paper trail of school expenses.

“Plans, signatures, oversight to make sure the vendor wasn’t overbilling, that they were delivering what they were supposed to, that the right people were doing the work — no records for any of that,” Stringer said.

Spending more on education is laudable — if the money is well-spent, said an expert.

“The question isn’t how much New York is spending; it’s where savings and waste can be identified,” said David Bloomfield, a Brooklyn College and CUNY Graduate Center education professor. “It’s more a management question: Do people have confidence in the mayor and the chancellor as managers? Those abilities have been widely questioned.”

Bloomfield cited the Absent Teacher Reserve, a longstanding pool of 1,300 teachers and other educators on the payroll without permanent posts because of school closings, misconduct or incompetence. Working as substitutes or doing nothing, they cost $100 million a year. The DOE is struggling to place or fire the excess crew.

He also cited Mayor de Blasio’s Renewal Program to fix failing schools, a money pit of contracts and consultants expected to cost $784 million through 2018-19.

After three years, the city has given up on 17 of the original 94 Renewal schools. Three schools met all improvement goals last year, while 61 declined in at least one category, The Post found.

Overall, higher spending has not brought similar gains in student performance, according to several measurements.

On the National Assessment of Education Progress, a congressionally mandated exam given every two years, from 2009 to 2015 New York City fourth-graders’ math scores sank 6 points out of 500, while reading scores dropped 3 points.

Eighth-graders inched up 2 points in math and 6 points in reading in the same period, but still lagged 6 points below the national average in both subjects. Fourth-graders trailed the national average by 7 points in English and 9 points in math.

While the city touts a graduation rate that hit an all-time high of 72.6 percent in 2016, test scores showed only half of those awarded diplomas were ready for college or careers.

Meanwhile, salaries are rising for the city’s 75,000 teachers. Under a United Federation of Teachers contract signed in 2014, top pay jumped from $100,000 to $119,000.

Teachers also won retroactive raises back to 2009, when their previous contract expired.

© 2017 New York Post