When I phoned Mary to tell her that I’d excluded her son Billy, she probably had the kettle in her hand. This is the only way I can explain her suggestion that I should shove a kettle up m... “Well, it is certainly not going up there, Mary. For a start, the lead’s not long enough.”

She slammed the phone down, and I sent Billy on his way. Mary can be fiery, but over the years we have learned how to handle her. Above all, we have learned who should do it. She is, after all, an ex-pupil. On this occasion though, I got it wrong. I should have left it to the head of year. At present, he can do no wrong and I am the Antichrist. Next term, we might well reverse roles, as we have done before.

As in many of our dealings with parents, I should have used my knowledge of personalities and circumstances. It is a skill that all teachers have, and goes largely unrecognised, but it underpins all that we do. Billy, for example, was born as a consequence of a liaison undertaken for a bet on a particularly dark night. Billy is aware of this - it is common knowledge - and this has scarred him and his mother. The exotic detail reinforces his status as a comic victim. It is a dark shadow that when trotted out is guaranteed to make Billy explode and liven up a dull lesson. Sadly, I can explain it, but I cannot prevent it happening.

It is interesting to speculate which comes first: difficult children or difficult parents? Certainly, there are parents who have a reputation, and only informed understanding can prevent a bloodbath. When Mrs Jones turns up, it is my job to calm her down before she crashes into the office staff. She hates them because they are all thinner and younger than her. Mind you, they don’t have her mesmerising tattoos; the variety and detail are hypnotic and can make concentration difficult.

Our school - surrounded by Fifties council housing - is far too accessible and thus impossible to make secure. So, unexpectedly, I came across Mr Noble, fetched to school by his son Jimmy, who arrived with eyes spinning like a fruit machine, looking to deal directly with the head of Spanish over his decision to make little Jimmy sit on his own for a test. I had to stand in front of him on the stairs, barring his way. He calmed down when I shouted at him. I have to say, it was a bit of a risk. This is one of the problems of working in an area of high unemployment: the parents are too easily accessible.

When Krystle has a row she is out of the gates, and two minutes later she is back with her mother. Or, even worse, her aunt. For reasons I have yet to explain, whether it is Kirsty or Karli or Kyle, Aunty is always an expansive harpy in carpet slippers. Also, as an ex-pupil, she knows her way round the school too well, so you can often find her or one of her fellow crones in the most unlikely of places, looking for vengeance.

Take Mrs Thomas, for example. She slipped the leash and slapped the head because the police wanted to question her son. The head was unlucky. He was the wrong person in the wrong place at the wrong time.

Certainly it is not unusual for parents to end up in a classroom, steaming, only to discover that they have been set up by misinformation from their child. Then the discussion can turn round completely and Mrs Thomas will start hitting her Nathan round the head. Suddenly, you’re protecting him.

Often their solutions to the problems that brought them up to school in the first place are simple. “If eez norty agen, Mr Brookes, then you ‘ave got my permission to give him a slap.” Of course, when you don’t follow this advice the parents think you are weak, and if the problems recur, well, it’s your fault. They did tell you what to do, after all.

Naturally, they can never come to parents’ evenings. They are either too busy or ill. I suspect, though, they would rather burst on to the scene in the middle of the day because they like the attention. It interrupts the monotony of an aimless day. It allows them to move to the centre of someone’s attention, if only for a brief moment.

My objective always is to get these unexpected visitors into my office. I need to ensure there is no entertaining public drama which the school could feed off for the rest of the day. So I am like a horse whisperer, soothing them. After a while, you develop an instinct about how you should react. Sometimes the mere sight of a man in a suit is enough. The suit represents status and as they have come straight to what they regard as the top, they are happy, because they feel they are being taken seriously.

Others, though, resent all forms of authority. Then you have to make a judgment whether to be firm or cross, whether to deflect or to give as good as you get.

Often you find that if you bluster or try to defend the indefensible, the aggrieved party can become even angrier. Sometimes it is better to say sorry, that the teacher got it wrong. It saves becoming involved in byzantine arguments, justifying what you know is wrong. But you must always expect the unexpected. In a close-knit community such as ours everyone can appear to be related to everyone else. So you can intervene in a pupil dispute only to discover it is a family affair. When such spats get out of hand you can have the parents banging on your door, trying to recruit you to their side.

Yet in all of this, in all the unpredictability and the absurdity, there sometimes comes an almost infinite sadness about the lives you encounter - lives stranded, lives wasted. There is the sadness of meeting Mrs Ball. Her son Jez has ADHD and is taking a heavy dose of Ritalin - as so many are. It wears off by 11.30am, so just before lunch he is no longer sedated and is often in trouble. The only solution she can see is to double his dose. As she sits sobbing in my office, I wonder what sort of future they both face, living with the chemical cosh.

And I can’t meet Lucy’s mother at all. She walked naked into the sea and was washed up three days later. Lucy has learning difficulties and still expects her mum to come home. But then, if it was me, perhaps I would be waiting for mum to come home, too.

School is just a part of children’s lives, and sometimes the rest of it can make that part deeply unimportant. However much we think we know and understand their circumstances, we do not. We don’t know even half. Suddenly, though, there can be an illumination, when children become a window into their lives. You sometimes wish they had closed the curtains.

Geoff Brookes has been deputy head of a Swansea comprehensive for 10 years