After 35 years of teaching, I can count the appalling parents on the fingers of one hand. The first may not have been the worst, but it felt that way.

It was 1974, two years after they raised the school-leaving age. I was in my first year of teaching and my form consisted of reluctant 15-year-olds. Despite my efforts, English wasn’t their favourite subject. Leading the oppositional pack were Yabad and Spam.

As well as tartan trousers and Dr Martens, the ubiquitous fashion accessory then was a metal comb with a sharpened handle - a deadly weapon. It was last period in the morning. Until the last minutes, Call of the Wild by Jack London had held the attention of the class - but not Spam’s and Yabad’s. Spam brought out his comb and tossed it to Yabad. Most of the class was still engrossed in the fictional wolf’s tale. I kept reading but walked towards the comb jugglers. By some miracle I reached out and caught it. “That’s mine,” I said. Then the bell rescued me.

That afternoon, I got a message to go the head’s office, where I was confronted by an older version of Spam. His father said: “Is this the wee runt that stole my wife’s comb? I want it back.”

“Let’s hear Mr Wood’s side of this,” my head said. After I’d explained the circumstances, he turned to Spam’s dad and said: “Mr Wood was justified. He had the class’s safety to consider.”

He threatened to have me charged with theft, all over a comb. The local police station, 150 yards south of the school, was visible from the head’s window, so he pointed to it. “Fine, and we’ll report your son for being in possession of an offensive weapon.”

The father left, muttering obscenities. Occasionally, negotiation is pointless.

The writer is a headteacher in Edinburgh.