What matters is not whether children are in reception or nursery classes but what and how they are being taught.

"Nursery education for every four-year-old," boasted last weekend's headlines, as the Government announced that it was fulfilling its manifesto pledge on the under-fives.

There will, of course, be nothing of the kind. Most four-year-olds will continue to be educated not in nursery schools or classes but exactly where they are now - in school reception classes.

Does it matter? The playgroups and some members of the early-years education lobby are anxious. They say there is plenty of evidence to suggest that starting school too young is damaging. Children in reception classes tend to be in larger groups with fewer teachers and less space than those in nursery classes.

Recently, a Channel 4 Dispatches programme found that other countries in which children start formal school at six or seven later outstrip our primary school pupils in maths and English. Instead of the the three Rs, the programme argued, younger children should be given a structured programme in speaking, paying attention, listening and using memory.

Last week, Margaret Hodge, MP, the forceful chair of the Commons select committee on education, backed the idea of a fresh look at the content of early-years education based on international evidence. Even ministers said they were looking again at the nursery curriculum guidelines that define what a five-year-old should be able to do. The latest educational snowball was off and away.

It is the most recent round in a debate which has raged for decades about the right way to teach young children. Crudely put, the divide is between those who think under-fives learn mainly through play and that formal teaching too young is damaging, and those who have no time for "sand and water" and think that teaching the three Rs should begin sooner rather than later. Under the previous government, the last group, led by Chris Woodhead, the chief inspector of schools, made some headway in influencing the nursery curriculum guidelines. Now the other side is fighting back.

The debate is important because what matters is not whether children are taught in reception or nursery classes but what and how they are being taught. Peter Tymms, of Durham University, who has just finished a study of 1000 children in 63 different reception classes and has embarked on another of 100,000 children, has found that most reception classes are good places to be: most children thrive and many make staggering progress that defies all predictions.

Some four-year-olds arrive in reception classes with some knowledge of letters and numbers, even though they have not been formally taught them. Are we really going to say that they should not be taught to read straight away? We know what works in Hungary and Switzerland, but do we really know enough about what works here to introduce a whole new philosophy of early-childhood learning that may prove just as damaging to some children as early formal teaching is to others?

A set of common goals that all children should achieve by the time they are five is one thing. A blanket approach that leaves children either frustrated or floundering is another.

Proper staffing is vital to give teachers time to sort out what individuals need. Ministers say they are insisting that local authorities ensure there are enough adults in every reception class. Their admission that some authorities still have some way to go is alarming. No four-year-old should be in a class of 30 with a single adult.

Equally important is the revision of the nursery curriculum guidelines. Beware the snowball. The educational history of this country is littered with examples of lurches from one extreme to another with hapless children caught in the middle.