She has watched them grow and change over the months, and, with wit and perception, charted the progress of some of the children - the flirty Fenella, who finally decided to answer to her name; her own son, Jake, who had to share her with the rest of the class - and observed the way the ups and downs of their lives are reflected in their behaviour at school.

Her column will continue once a month.

Class 5 are playing shop. You would think that this was one of the most basic rituals of modern life and that Year 1 children would not need initiating into it. You would think that they might have pocket money and that they would have an idea of the prices of things and that you get change. But you would be wrong.

As Mrs Peach, their teacher, says, it seems that they “tag along” when their families visit shops. Their recollections of supermarkets are confined to bargaining for sweeties, riding in the trolley and the bad behaviour of siblings.

“Do you go to the sweet shop?” I asked my helper in the shop. She beamed. “Every day.” “What do you get?” “Cigarettes.” I tried another tack. “Do you have pocket money?” She frowned. “What’s that?” This week the class went shopping. They went to the local supermarket and recycled their tins, papers and plastic bags. Then they went off and spent 10 pence at the sweetie shop. I was mortified to find that the child best known to the shopkeeper was my own.

Perhaps I am upholding a lone tradition of weekly pocket money and teeth-rotting. As one very proper mama said to me, “We have sweets. We have one finger of Cadbury’s Fudge on Saturday.” Personally, I prefer a bar of Swiss chocolate but I know Jake likes a pair of pink teeth, some lips in red, a sugar necklace, flying saucers and a liquorice bull’s-eye. He’s also one of the best at mental arithmetic and has no fillings. So there, Mrs Perfect, I thought.

An air of contentment settled over the class as they munched their way through their goodies and tongues were still curling reminiscently around mouths as they wrote their account of their purchases. Perhaps the old Jewish custom of daubing the slates of children with honey so that they should think study was sweet was a good one.

Strangely enough, however, the sums of these children still did not always add up. So much for educational theorists who believe that if motivation is sufficient, ability will quickly catch up.

In our pretend shop, Jed, who has special needs, wanders in. He jumps the queue. The others object. He ignores them. I rebuke them and send him to the back of the queue. He goes to the back of the queue - and out of the shop. He is sent back by Mrs Peach. He wanders round the shop, upsetting the displays of puffed-up but empty crisp packets, Plasticine lollies and balloons.

I can’t deny it, he is a nuisance. On the other hand, he is the only child in this group of six who understands the concept of change. I praise him for this. He is uninterested and wanders off. The other children giggle. I rebuke them. Suddenly the day seems unbearably long.

Then Robert appears on the scene. He is mad keen to buy something, anything. “But have you got any money?” I ask, sorting through a heap of paper 20 pences. No, he hasn’t any money. In fact, he isn’t supposed to be here. Mrs Peach arrives to lead him back to his designated task of writing his news. His face crumples into tears. I see her comforting him with the words, “Yes, I know you wanted to be part of it. But the other group are doing it now. You’ll have your turn later.” He sobs, his shoulders heaving. I feel like asking him back, but see the sense of her remarks and we continue.

Fenella wants to give her friend Maria a Pounds 50 note for change. It is hard to explain why that is a bad idea if the person you are talking to does not seem to understand the difference between pence and pounds, or possibly even between 10 and 11.

Barry wants to give me all his money, although his purchases only add up to 12p and he has 50p. “You ought to keep it for another go later,” I suggest. He looks at me in surprise. “But it’s not real money.” Fenella goes dreamy. She is stroking a flowered shopping basket. “I like this bag,” she croons. “I like it, it’s my sister’s.” Later, I idly ask Mrs Peach about the flowered bag. “Oh no, it’s not her sister’s. I think she just likes it.” I stare at the flowered bag, bemused. Still, I don’t like flying saucers, sugar necklaces or Cadbury’s Fudge, even if I do know how much they cost.