7am: Any minute now the phone will ring and I will be sent over the hills and far away. I sometimes think that schools believe that supply teachers sit ready and waiting at the agency office in a long line. And like a row of Mary Poppinses, when summoned we twinkle our eyes merrily, point our umbrellas to the sky and while singing, soar gracefully towards the required location.

7.15am: Am making tea when the phone rings. Am most un-Mary-Poppins like. In a bleary and distinctly non-twinkly manner, I pick up the receiver. Do I want to go to Aberhyddan for the day? Don’t know where it is but I know it’s not near here. They offer me Romily High as an alternative. Would rather gouge out my own eyes with a rusty teaspoon, so agree to Aberhyddan. Write down elongated directions on the back of a gas bill, involving numerous pubs, petrol stations and other places of interest.

“Can I get there by 8.30?” the girl asks brightly. How the hell should I know? Never been there before have I! “I’ll do my best,” I assure her, watching a herd of pigs fly past the window. Wonder vaguely if all these flying pigs are responsible for the recent outbreak of swine flu. It is a very long drive. Am singing, “I’m on the way to “Aberhyddan” to “Amarillo” tune, when realise with horror that I may well be turning into Ms Poppins after all and check mirror for tell-tale twinkle.

8.25am: Am safely at the school having driven through four different counties and as many weather zones. The newly built main building is sleekly chic with grey stone and tinted glass. Am given a tantalising glance of the new library and staffroom before being shunted off to the languages block; a rickety looking demountable, aka a “hut” or “terrapin” as they were called when I was at school.

It is situated in a sad and boggy place that Eeyore would have been proud to grace. A gaggle of disconsolate, soggy shapes in black windsheeters are waiting. Typically, it is locked and I haven’t been given a key. Ten minutes later and am dislodging my heels from the mud as the caretaker arrives to let us in and turn on the heating. Two girls dramatically throw themselves over the wire fireguard in a bid to be as close to the heater as they can and to grab all possible warmth for themselves. They are reluctantly persuaded to sit down after I agree that, yes, it is wet and “minging” and cold.

9.15am: The lesson is underway. It is a Year 9 Welsh class. I congratulate myself for helping a pupil, remembering that “egwlys” means church as it is similar to the French word eglise. This encourages other pupils to ask for help and I am quickly exposed as a fraud with no real knowledge of Welsh at all.

“Well, I can speak French, German and some Spanish,” I say in my defence. They remain unimpressed, except for one boy at the front who wants me teach him swear words in German. “What does schweinhund mean?” he asks.

“Well, literally, pig-dog, but it is very rude to say that in German,” I admonish him.

“What about scheisse?”

“Never heard of it,” I lie.

He keeps on pestering me to tell him. In the end I teach him how to count to three in German, just to take his mind off the swear words. He is delighted and keeps shouting, “Eins, zwei, drei!” like a demented game- show host.

11am: Am in a draughty lab with a GCSE physics class - double lesson. “Are you a science teacher, Miss?” asks one pupil.

“Um no, I’m a languages teacher,” I reply truthfully.

“Well, what you doing here, then?”

A very good question.

1pm: Lunchtime and am in the ultra-modern staffroom drinking coffee. I scan some of the notices on the board: netball practice, report deadlines, photos of children who have nut allergies - one of them cannot even be in the same building as a nut. Look at NUT poster about a march to protest against full-time teachers’ pay. Wish they’d do something about my rate of pay. Am professional person being paid peanuts. Look back at photos of allergic pupils: “Don’t become supply teachers,” I mentally advise them.

3.15pm: Am walking towards my car. The sun is shining, albeit weakly. Am wondering if I have actually achieved anything at all today, when a familiar voice chirps up: “Bye Miss!” He flashes me a huge grin and runs off shouting, “Eins, zwei, drei!” punching the air with his fist. As I drive through the gates there is something resembling a faint twinkle in my eye.

• Jo West, Supply teacher, Cardiff.