A few years ago, following a well established fancy dress tradition, the star rider in our cycling club turned up to the Boxing Day race in a gorilla suit, riding a delivery bike with a basket of turkeys on the front. And, of course, in spite of his handicaps, he still won the race.

On this principle - that a committed expert can produce results despite all difficulties - hangs the great dilemma of school funding. Put a good teacher into a classroom with 50 children, a stick of chalk and a bible and she will teach them to read.

What does this mean? Has she demonstrated that she is worth investing in, because she could clearly do even better with proper equipment and a smaller class? Or has she proved that small classes, expensive reading schemes and classroom helpers are luxuries we can do without?

Heads of schools with big classes - and there are lots of them given that now there are a million children in classes of more than 30 - are acutely aware of the political danger of demonstrating that their teachers can cope. Philip Marples, head of Sonning Common Primary in Oxfordshire, has won over doubtful parents to acceptance of a top junior (Year 6) class of 41 children -helped considerably, I guess, by the fact that his own daughter is in the class. He voices a common concern when he says, “I’m worried that someone in government will say ‘There you are! You’ve taken a positive approach with a lean budget. ’” Perhaps his staff could cope for a while, but if it went on for three or four years, “I wouldn’t like to think what the stress might be on the class teacher.” It is a point Mr Marples has made, with other local heads, in person, to the local Member of Parliament, Michael Heseltine. (The phone number of the First Secretary of State and Deputy Prime Minister, I noticed was on a Post-It stuck to Mr Marples’ phone. (“He gives his time, and he listens, but . . .”) The Sonning Common story also shows clearly what most teachers will readily admit - that class size, though a convenient measure of resourcing which is very intelligible to parents, is not a straightforward issue. It would be quite misleading, for example, to suggest that Sonning Common’s Year Six teacher spends the whole of every day alone with her class.

For three mornings a week the deputy head is in the room with her, and for the rest of the time there is usually a classroom helper. Add the head’s music lessons and the French lessons, and the picture starts to look less bleak - which, of course, is exactly why the parents accepted the package for this September.

The working atmosphere which I experienced in the room would satisfy the sternest critic. But those extra hands all cost something and come from the school’s finite resources. Half of the French teacher’s time is paid directly by a voluntary levy on the parents, and the more time the head and the deputy (who is the special needs co-ordinator) spend with the class, the less time they can spend elsewhere. One direct effect is a reduced programme for bright children instigated and led by the deputy head whose role in it this year has had to be reduced to consultancy and organising resources.

Visiting the school I suddenly realised I was seeing two classes being run as one, because separating them would require another full-time teacher. Indeed, Philip Marples acknowledges that a couple of years ago he could simply have put two teachers into this year group. Neither does putting lots of high quality support into a big class take all the problems away. Sue Tyldesley, the class teacher pointed out that although planning and marking can be shared, she has the overall responsibility, and must keep an overview. She keepsthe register, and she is the person that parents will want to see at interviews about pupil progress. “Someone,” she says matter of factly, “has to be in charge.”

Sue Tyldesley will also have responsibility for preparing the children’s records for transfer to secondary school. “There’s one for each core subject and a pastoral record - four in all for each child. We have to get on to them right at the beginning of the summer term because the secondary school likes them before the half term.”

Each of these records, it turns out - and she says it quite casually - “takes about an hour for each child.”

In other words, this teacher, will fit at least 40 hours of additional paperwork - a whole extra working week - into the six weeks of the first half of the summer term (which is when the Standard Assessment Tasks have to be done, incidentally). During that time she will try at considerable personal cost, to keep up the quality of the work in her classroom - thus reinforcing the notion that class size has no bearing on pupil achievement. Here, perhaps, is the pedagogic equivalent of turning up to a bike race in a gorilla suit.

One way of keeping class sizes evenly spread across a primary school is to run mixed age group classes. Opinion on this is clearly divided. Some schools - Sonning Common is one - go to considerable lengths to keep year groups separate. Others see positive advantages in the kind of vertical grouping that small village schools have always used. The usual assumption, though, is that a mixed age class needs to be smaller still. In any case heads feel that the choice, within limits, ought to be a matter of professional judgment rather than of financial expediency.

To be fair, David Rule of The Queen’s Dyke primary in Witney, which has three classes mixing nine, ten and 11-year-olds (Years 5 and 6) with 36 in each, plays down the idea that the vertical grouping in itself makes the job more difficult. “It’s an awful red herring. If you have a single age group class there’s such a range already. Even if you take something as crude as a reading age score your range of ability is pretty wide.”

All the same, he would not have deliberately chosen his present position. For most of the last school year, he and his colleagues were planning to run an extra class - making 14 classes - this September. The school has grown a lot. Last January it had 20 more children on roll than in the previous year, and this should have produced the finance for a fourteenth teacher. Oxfordshire schools, however, in common with many around the country, then suffered an overall budget reduction which neatly wiped out the expected staff increase.

I met two Queen’s Dyke upper junior teachers. They spend most of their time alone with their classes, and the story they told will be familiar to their colleagues across the country - of the need to be highly organised, of the constant worry about children with special needs (each class has a dozen or so identified special needs pupils with individual education programmes), of the difficulty of running a sensible, national curriculum-based gym lesson in the hall with 36, of the struggle to keep up with marking, and of the need to run four parents’ evenings instead of three. “We’re doing everything we can so that standards won’t slip,” said deputy head David Haley who is also a year 56 teacher.

Given the difficulty of controlling the variables, research on the effects of class size is probably always going to provide results which are open to interpretation. All the same, the feelings which teachers - and, importantly, parents - have in their bones are based on experience of real children. It is class size, after all, which is the biggest influence on parents opting for private education where classes are invariably smaller.

Ann Pearce, parent of a girl in Sue Tyldesley’s class at Sonning Common, has the kind of worry that many parents share. “I have a daughter who’s a people watcher. And in a big class there’s always something for her to look at - something to cause a distraction.”

Her instinct is to trust the school but to be wary of what happens in the future. “There was a lot of concern at first, and if the class didn’t have that extra support there’d be tremendous anxiety.”

Teachers emphasise that a busy classroom is not necessarily a productive one. Ann Wilkinson, of Chaucer Primary in Fleetwood who in the past three years has had a reception class of 40, a Year 3 class of 38 and a Year 3 class of 34, feels that making this distinction is the real challenge for a teacher. “The tasks they are doing have to be meaningful and you have to monitor their learning.” She reeled off all the obstacles to this in a big class: the lack of space for a quiet corner; moving the furniture to have circle time.

What really gets lost, though, she believes, is simply the amount of time that the teacher has for each child, not least for the kind of social talk that seems trivial but which strongly reinforces the child’s commitment to the teacher and thus to learning. “It’s important to listen to what they are saying to you. If a child comes to say something and you send them away, what kind of message does that give?” Teachers feel, with justification, that class size is a good meeting point of concern with parents. The women at Sonning Common, though, talk not only of their anxiety about class sizes, but of problems across the whole of the age range. “My youngest child will be five in January and won’t start school till Easter,” says Ann Pearce, while according to Christine Bradley, “Nursery places in this area are like gold dust.” Another parent, Ginny Merricks, mentions that the local secondary school head has written to parents asking for a donation of Pounds 10 a month. There is also talk about the costs to parents of students in higher education. All this from just three parents gathered in a room in South Oxfordshire.

Education is investment in future prosperity. Giving credence and strength to this familiar soundbite has become a mission for Philip Marples. “Michael Heseltine says that we have to consider the macro-economics - that we have to be able to afford it. To which my response is that education, in the final resort, decides whether this country is going to do well or not.”

So, undaunted, Philip Marples now reads as much background as he can, keeps Mr Heseltine’s number handy, and mentally arms himself for the battles ahead. And battles there will be, for behind much of the anxiety is the certainty that local authority budgets are going to shrink even further. As David Rule puts it, “If this is our baseline now, then next year is going to be horrific. ”

Ann Pearce sums it all up in words that ought to give pause to teachers and to politicians of all colours. “I worry a lot about my children’s education. The children in Year 6 were the first ones to take the SATs at seven, and I see them as guinea pigs all the way up. I fear that when they get to 16 someone will tell us that it didn’t work after all.”