In my school, law and order have gone the way of the slide rule.

I am a math teacher at a middle school in Flushing, Queens, and two months ago, I was helping one of my students work out an arithmetic problem when he called me a “f–kin’ asshole.” When I asked for an apology, he shoved a chair at me and stormed out.

Five minutes later, an administrator brought the student back to class. She informed me that she had called his parents and that he could return.

And what did I do? I went on teaching.

In my 20 years working for the Board of Ed, I’ve never seen such a disregard for the rules — and human decency — as I’m seeing now.

Smoke weed on campus? Grab your fellow student’s breast? Tell your teacher to f–k off? You just earned yourself an in-house suspension — also known as a hang-out-with-your-phone-in-an-empty-classroom day.

When I started out, an altercation with another student could get you an out-of-school suspension ordered up by the principal. Nowadays, giving a kid a bloody nose doesn’t even buy you so much as an in-house one.

And the kids are so street-smart, they know exactly how to commit the maximum amount of crime and get the least amount of time.

If I tell a student to put away her phone, the conversation usually goes something like this:

Student: “Leave me the f–k alone.”

Me: “I’m going to call your parents.”

Student: “I don’t give a crap. My parents will just agree with me.”

Then maybe she’ll throw a desk across the room for good measure.

So now the trend is that the good kids, the kids who do their homework, who pay attention, are seeing this and asking themselves, “Why do I have to be good all the time?” And now they’re misbehaving, too — because, well, why not?

So what can we teachers do to lay down the law? Under the current system, nothing. The best we can do is meet with the troubled kids and try to explain that their actions have long-term consequences. Consequences that, as adults, could be fatal.

Every now and then, it works.

But try explaining life to the kid who repeatedly got reprimanded this year — mostly for sexual harassment.

And all he got was a string of in-house suspensions.