I came back to education rather late in life - just turning 50. I had disliked school from day one. Learned to read and write, and that was about it. I knew I would never return after age 16. But life is funny, and when I found myself a has-been at 49, I had to look outside the comfort zone I had built up with 30-odd years of writing and editing. In fact, it was my wife who looked outside my comfort zone. She had always had a strange belief that I would make a marvellous teacher. Where she got this notion from I have no idea. It was she who applied for me on seeing a job advertised for a cover supervisor at the local comprehensive.

From September 2004 the government and Nasuwt decreed that all schools had to make sure teachers would do no more than 38 hours of cover (taking lessons for absent colleagues) each year. And so was born the position of cover supervisor, a full-time job covering lessons across the whole curriculum for teachers absent through illness or coursework. A masterstroke of the government and the education system was that the position called for no qualifications or even training, allowing for a minimum wage.

No qualifications or certificates in hand, I applied for the post. When called in by the headteacher, I was upfront about my lack of qualifications. Regardless, he took a shine to me and, to my amazement, I was offered the job.

"I can't do maths, you understand," I protested.

"You'll be fine," he assured me.

He's the head, I thought. He must have spotted some quality in my character hidden to all but him and my wife.

Haircut and suit. September 6. Back to school. I'm the new boy, aged 50. My first cover lesson: maths.

"Sir, what's this mean?" asks a 12-year-old. I look. Gibberish covers the page of his text book.

"This is looked on as a revision lesson," I explain. "When your teacher returns he needs to be able to see what you don't know as much as what you do know." Pretty cool on-the-spot thinking. I'm convinced. Unfortunately, the boy isn't. "He doesn't know," he whispers to his mate.

Nor did I. I also didn't know science, geography, French, German, DT, business studies or cookery, but soon found myself holding lessons in all of them between three and five times a day. For the year and a half I was at the school, not once did a teacher step into a class to observe how or indeed what I was doing. A lot of cover lessons would degenerate into handing out word searches.

"We've done this!"

"Three times already!"

"Then it shouldn't be too difficult for you!"

The students knew this situation didn't quite add up. Speaking of adding up, I often wondered just how many cover supervisors there were up and down the country taking countless lessons each term. We are looking at hours and hours taken out of each student's lesson timetable. They might as well have been doing dot-to-dot puzzles. Hearing the government claim it had put x number more teachers into schools made me gag. The con being that we cover supervisors were on a puny wage, so hasn't the government done well, a zillion more teachers at half the cost.

During my time at the school I was attacked three times. Once with a hammer. Fair dues to the lad, we were in the woodwork area so he was using the correct tool. The second attack was with a carving knife, and again praise to the boy involved as I was taking a cookery lesson at the time. My favourite incident was when a 14-year-old girl walked across my science class while unwrapping a Black Velvet liquorice-flavour condom.

"Do you want to use this on me, sir?"

Again full marks for politeness and sexual responsibility. As an untrained teacher I recognised the minefield that lay before me with whatever response I gave. Amidst sniggers from the class I simply told her to get back to work. When I reported the incident later, the head's reaction was: "She can be difficult."

He also came down like a ton of feathers on hammer-boy, giving him a two-day suspension which, since he spat at me on his return, didn't seem to have the desired effect. Knife-boy had to write a letter of apology to me in which he promised it would never happen again. So that was all right then.

It was strange to mix with teachers in the staff room. Certain social skills seemed missing from the majority, particularly those who had gone straight from school as students to school as teachers. On my first day in September, one of them had given me the often-heard tip: "Don't smile until after Christmas." Although I had little to smile about, I found this an impossible task after a lifetime of smiling like a loon. It is obviously a skill acquired during teacher training. The majority of teachers were stressed and unhappy, with paperwork and lack of support being the main problems moaned about daily.

During my first term, there was concern from the more militant teachers over my position as the uneducated teaching the uneducated. Unions were mentioned, but nothing came of it as I was soon covering so many lessons each day (three to five out of five) that it made life easier for the staff.

I did snap once. I was holding a science class for the dregs of the school. As text books and beakers flew every which way, I bellowed that they were a "bunch of tossers". Silence. And then: "You can't call us that. We're going to report you." My only thought: "Please go get me fired."

Angry parents phoned the head demanding justice for my slur on their family escutcheon. Writing out an incident report, I exchanged the word tosser for dosser and no more was heard about it.

Ofsted inspectors came to the school. It was interesting to see that they didn't come into lessons covered by me or my fellow cover supervisor. The school was deemed "good".

Not a week went by when I wasn't astounded at school life. On the way home one evening, I spotted a student happily scrawling the initials KKK on a town landmark. When I brought this up with the head, he just shook his head. "Nothing we can do if he was outside the school." No feeling of duty to educate the boy on the full wonders of the Ku Klux Klan.

One day I was holding a class in RE when my mobile rang and someone offered me some freelance writing work. The class was quite out of control, with Bibles being hurled out of the window. I felt I was either going to strike a child or a teacher at some point soon. I had to go.

The students remain, preparing for tomorrow's bright new world. Cover supervisors continue holding lessons - up to GCSE and A-level - for which they have no training or qualification. Children deserve better.

· The author is writing under a pseudonym