Can I buy you a drink Mr Cairney?” the twentysomething asked, displaying a serious aptitude for superfluity. Before I delivered the inevitable response I looked at him closely, and from his age and the respectful use of the “Mr” I assumed he was a former pupil, but recognition was not immediate.

On these occasions I waffle for a bit and play for time to identify a school, an era, a face, a family resemblance. Generally I am able to avoid the worst case eventuality, but not this time.

“I’m sorry, son, but I just can’t place you.”

“Oh it wasn’t me you taught, it was my father.”

Meeting former pupils is for most teachers frequently pleasant, occasionally gratifying and sometimes embarrassing. This, however, was a first. I assumed his old man would have been in one of the first two categories or the offer of a drink would not have been made. The son got more than he bargained for, because when he discovered that I was with my wife and a friend he insisted on buying all of us a refreshment.

I experienced the other end of the social spectrum some years later when I walked into a lounge bar to meet some of my colleagues (and, no, I don’t meet all my former pupils in licensed premises, but come on, this is Glasgow we are talking about here).

Sitting among them was a blast from the past. This young chap had been a very naughty boy - often. This was no time to harbour old grudges so I offered him my hand (to shake). He was unreceptive. “Hey, Cairney, you pushed me once.”

He was quite right. It happened after I caught him grabbing a much younger pupil and threatening him with physical injury. This was in the days when schools had as many anti-bullying policies as there were members of staff. My policy was rudimentary: how would I respond if I saw any of my own children being treated like this?

I tried again, offering him my hand, but he recoiled. My reply was brief, to the point and unprintable. I wasn’t in the mood for this kind of unpleasantness and tension at the beginning of my Friday evening out, so I bid my colleagues a reluctant farewell and headed for the bar across the street where the beer was more expensive but the company less disagreeable.

Two days later I learnt that my surly antagonist had been bared from the pub for persistently pestering customers. An added twist was that the pub manager who barred him was also a former pupil, and another one who still insists in calling me “Mr” even though he is in his late thirties.

It was about this time that I came across some of my former charges at a church service. I had accepted an invitation to sing in a staff choir that would assist at an Easter service. We may not have been very musical but we found that we had to turn the volume up to make up for the fact that the all-male congregation were extremely quiet.

From my position at the back of the stalls I managed to identify at least two people in the pews that I had taught, though they didn’t seem too keen to make eye contact with me - perhaps it had something to do with fact that the service was being held in the chapel in Barlinnie Prison.

There have not been many distinguished alumni that I can recall meeting - distinguished that is in the sense of achieving national recognition of a positive nature, though I dare say a certain young Glaswegian new Labour MSP who was a housing minister in the first year of the Parliament only to find himself sidelined in last year’s reshuffle would not agree.

There have been, however, countless young people I have met who have made good, constructive and socially useful lives in areas ranging from senior interpreters in the European Parliament, to television and radio scriptwriters and gynaecologists, to the man who drove the local authority gritter during the recent blizzards and the part-time postie who came to my house to ask my advice when he discovered he had lost the keys for the local post-boxes and was scared to go back and tell his gaffer at the depot.

Recently I was asked by a group of former pupils, all now in their forties, to help organise a function next year to commemorate the 30th anniversary of the opening of my last school. That should be quite an occasion. It’s a pity that the organisers can’t get to hold the do in the school, as we did for the 20th, but the school, perhaps like some of its erstwhile occupants, has changed greatly and the new (private) owners won’t allow it.

The last words I will leave to the father of the young man who bought me the drink. “I have two things to thank you for Mr Cairney. You taught me to swim and you taught me to dance.”

I’ll settle for that. Cheers.