United Federation of Teachers chief Mike Mulgrew reportedly is crowing that almost 97 percent of city teachers rated “effective” or “highly effective” this year. As well he should — since it means he’s succeeded in making the evaluations a joke.

After all, how do you have so many effective teachers when so many kids can barely read?

Officially, the latest number is 93 percent — for 2016. And the city Department of Education hasn’t yet sent the state Education Department the 2017 figures. But Mulgrew has lots and lots of inside pals at DOE: Heck, thanks to Mayor Bill de Blasio, he practically runs it.

But control of the headline numbers doesn’t change the fact that two-thirds of city sixth-graders can’t read at grade level and three-quarters of eighth-graders can’t do math at grade level.

However effective the teachers might be, the school system plainly isn’t.

Even supposed good news turns out to be hollow. De Blasio has made Advanced Placement classes and tests available to more high school students, so a third of the Class of 2017 took an AP exam. But only a dismal 18 percent passed at least one of the tests.

In most places, an 82 percent failure rate gets your program shut down.

Similarly, high school graduation rates are creeping up — but most grads aren’t actually college-ready, and have to spend the early part of their collegiate careers taking non-credit-earning, tuition-eating remedial courses. Which is a big reason why many don’t finish college.

Want another sign the system serves vested interests, not the kids? The new OpenTheBooks.com study reveals that 694 of the city’s 775 school custodians earned $100,000 or more last year — with many outearning the principal.

The inmates are running the asylum.