No prizes for guessing which gets the most attention.

In a class of 12, you can’t run, you can’t hide, and you can’t get by with homework produced in two minutes flat while barely dragging your eyes from Neighbours. However you enjoy a stress-free atmosphere, and even some of those near-extinct classroom pressures have humour, spontaneity and digression.

Cut to the child in the class of 34.

Here she comes, out of school, with a scowl like an ink line between her eyes. She has a headache. So, she says, does Sarah, and so does Lindsay, and so does Mrs Brady.

None of these headaches is surprising, particularly Mrs Brady’s, since she, poor woman, has to teach this enormous class of first-year juniors - including the usual (ie growing) number with behavioural and learning difficulties - in a room which appears to have been designed for a dozen malnourished dwarfs.

On the way home, there is a great unburdening of woes - the child’s ink rubber has gone missing; when she asked Mrs Brady about something-or-other, Mrs Brady didn’t hear her; Christopher Jones interrupted all through reading yet again . . .

It was never like this when she was in a smaller class, in a light and airy classroom, but now this outpouring is as necessary to her as the nightly gin and tonic of the stressed executive.

Then, at home, the next stage of decompression: the daily nit check, since in her crowded class the lice skip merrily from head to head, quite undaunted by the huge amount of money we parents throw at them in the form of lotions, potions and shampoos. Only after this can she run off, brow cleared, to enjoy the rest of her day.

Yet in spite of everything, she enjoys school and is well taught. At times - a true miracle, this - she is even lit up by what she is learning.

Far worse was the year her brother once spent, in a much smaller class but with a teacher so incompetent that the pupils ran riot, nothing was learned, and he chewed off the cuffs of his sweatshirt in frustration.

No, given the choice between a large class with a good teacher, and a small class with a lousy one, I’d choose the former every time. Apart from anything else, however low the numbers get, class chemistry will always be a volatile thing. Parents know they are lucky if their child hits a “good year”, full of well-adjusted pupils from happy, supportive families. A “bad year” can blight a pupil’s whole school experience.

For all these reasons, I have some sympathy with the Government’s stance that there is no clear relationship between size and performance. The research remains ambiguous, especially when trying to quantify the benefits of reducing class sizes at the margins, rather than cutting them significantly (and at prohibitive expense) to, say, fewer than 20.

But where the Government goes wrong, is in thinking that performance is all that matters. Most parents put their children’s happiness far above any test results, and one reason we so dislike big classes is that every day we have to deal with their consequences. If my daughter falls behind in maths or spelling, I can help her. But I am helpless in the face of her headaches or frustrations, and there is nothing I can do about the way she is learning to be a tiny cog in a big machine; or about what that, in turn, will do to her behaviour and expectations.

Research in Tennessee, which followed 7,000 children through their primary years, shows that drastically smaller classes do indeed have an effect on learning.

But, perhaps far more significant, is the effect found on children’s self-confidence, and their later willingness to take part in lessons, music and other activities. Because just as travellers in packed tube trains learn to stand like statues, rigidly avoiding all eye contact, so children in crowded classes also learn herd behaviour.

They learn to keep the noise down, follow the rules, “hurry up there, at the back”, wait for the computer, wait for everyone to get changed for gym, wait for them to get changed back again, jostle for desk space, and - despite furious arm-waving - never have much hope of that glorious moment of limelight when they get picked to answer a question.

Is there any “natural” class size? I feel there is. The recent survey by Neville Bennett of Exeter University shows that, generally speaking, parents with children in class of fewer than 25, tend to be happy, while parents of children in classes of more than 30 - now, one in five of all primary pupils - tend to be unhappy.

And, it occurs to me now, the only one of my children whose class size did not trip off my tongue when I came to write this column is the one whose class is somewhere in the low twenties.

And presumably that’s because, like the bear’s medium bowl of porridge, it feels exactly right.

Hilary Wilce’s new column is to appear monthly