Ican’t say that Marc Bruno had his illusions shattered. Any naiveté had been pounded out of the Riverside Institute of Technology teacher long before he got kicked in the head.

Bruno, a social studies teacher, got booted last week while holding back a 10th-grade girl after she tossed a metal chair at her boyfriend. He loosened his grip for an instant and … bam. The kick left him dazed, but not confused.

“People would be shocked if they knew what we have to deal with here,” he told me.

Forget, for a moment, the masses of flunking Buffalo kids. The under-the-rug issue, at Riverside and other schools, is a lack of discipline. Without law and order in the class, learning is a long shot.

Coincidentally, I sat down with Bruno and a few other Riverside teachers last spring to talk about chronically absent kids. The conversation turned to “Kids Gone Wild.”

“Just about every day, I see a kid in the hall and tell him to get to class,” said Chrissy Hall, a guidance counselor who has since left Riverside, “and he’ll say, ‘[Bleep] you, [expletive], go do your job.’ ”

What happens to those kids? Nothing.

“We’re like cops who can’t arrest you,” Bruno complained. “Students know there are no consequences.”

The blow that Bruno took last week – and the steak knife that security took off the girl who attacked him – underlined what he and the others told me last spring.

Authority loses its muscle when kids are free to f-bomb teachers. Rules lose meaning when students show up whenever for class – if at all – and don’t get punished.

It is no way to run a school district.

Bruno is not a crackdown guy. He likes to talk things out with problem kids. But he knows that “crime without punishment” does not work for teachers. It does not work for the majority of kids, who want to learn. And it does not work – in the long run – for the malcontents who think they are running the show.

“When these kids go to get a job or sign up for the military,” Bruno said, “that’s not how it’s going to be.”

Bruno said that things are getting worse. Complaints about the glut of suspensions for nonviolent offenses prompted district officials to tell principals to ease up. Untenured principals, worried about their jobs, are afraid to crack down on problem kids – or to back teachers who do.

Only a few schools, Bruno said, have principals who will take the teachers’ case to City Hall.

“You can write kids up [for cursing or not showing up],” Bruno said, “but nothing happens.”

I know you can’t suspend a kid every time he makes a face. But whatever happened to detention?

There has to be a middle ground between doing nothing – which destroys discipline – and exiling problem kids.

Bruno remembers a time when no suspended kid was allowed back in school until a parent met with the principal.

Ain’t that a kick in the head.