Education: How they put a price on a pupils head: Karen Gold reports on the furore among headteachers over the gulf in funding between primary and secondary schools and, below, examines how the money is being spent

Sceptical primary school headteachers call it the summer holiday miracle. Every year in mid-July each of their 11-year-old pupils is worth roughly pounds 1,000 of public money. Six weeks later, on the very first day that those same 11-year-olds set foot in secondary schools, their value mysteriously leaps to around pounds 1,500.

Although the figures vary from county to city and Labour to Conservative authorities, the pattern of funding per pupil throughout England and Wales is remarkably similar. Whatever the politicians give their primary schools to spend per pupil on teachers, books, equipment, facilities and everything else, they will give their secondary schools almost half as much again.

It has gone on for generations, ever since young children were taught the three Rs in classes of 40-plus by female teachers, while older children paid or were selected to stay on at school, had higher academic or technical status, and were taught by men. Periodically, primary teachers and experts complained, to little apparent effect.

But suddenly the system is causing a political furore. Groups of primary heads are springing up all over the country, claiming they are being underfunded. Local education authorities are setting up studies to compare the costs of what really happens in primary and secondary classrooms. And the House of Commons education select committee is investigating the disparity in funding.

The reason is the Government's insistence that local education authorities hand over education money to schools to spend as they choose. In deciding how much money to give each school, most authorities simply kept to their old pattern. When they published their decisions, primary schools could see for the first time exactly how much more in pounds per pupil their secondary neighbours were receiving.

'The primary heads were jumping up and down, saying 'You can't give us a system like this',' recalls Alison Kelly, an education officer in Stockport, who headed a local study into how the costs of teaching and equipping pupils aged four to 18 could be fairly compared.

Secondary teachers and heads made the same case to her that has since been made across the country: 11- to 18-year-olds take up more space, their school day is longer, they have science and language labs, more expensive specialist equipment and books, all of which must be maintained by technicians and librarians. For safety in science and technology, pupils must be taught in smaller groups. Most secondaries are larger than primaries, which means they need higher-paid managers and specialist staff, and so more money for salaries. Secondary teachers need more time for marking, writing reports, giving careers advice and dealing with adolescents. Secondary schools have to offer options, particularly for A-levels, so they inevitably have smaller classes.

But, say the primaries, all this ignores the national curriculum revolution in primary classrooms. All primary pupils now study science and technology, too. They need the equipment and closer supervision that is only possible in smaller classes. Every primary teacher now has responsibility for one or more subjects, so they need more time away from pupils even if they get no more money for it.

Four- and five-year-olds require as much social care as adolescents; the nines and 10s will soon be expected to have specialist subject teaching, too. The days when primary teachers set no homework and did no marking have been replaced by government and school assessments. And the earlier the system picks up and treats social or academic problems, the less they will cost to put right later on.

In Stockport, says Dr Kelly, those arguments tended to balance each other out. So when everyone had stopped arguing, they calculated the cost of a reasonable week's work in each type of school, and plotted the results against the money schools receive now. The outcome was clear. Funding for sixth-formers is about right; the 11-16s are underfunded; but the shortfall in primary schools was twice as great as that in secondary schools.

At this point it becomes a question of money and politics. Research among Sheffield schools by the Open University shows that it would cost pounds 12m in that city alone to cut primary class sizes to the size of secondary classes and give primary teachers the same lesson-planning and marking time as secondary teachers get.

In the past two years, some authorities have made small shifts in the ratio, usually by cutting primary school budgets less than they cut secondary ones. They want the Government to lead the way by changing its spending-per-pupil guidelines in money it gives to LEAs. The Government says education spending is a local decision.

Meanwhile, primary and secondary heads battle behind closed doors, while officially insisting that one set of pupils should not lose for another's gain. They are only too aware, says Peter Downes, head of Hinchingbrooke High School in Huntingdon, of the pitfalls of disunity: 'It would be a political diversion to get us fighting each other and a great danger, because it would obscure the main issue, which is that the funding of education in this country is getting worse.'