Class size makes no difference to education standards except for the youngest children, says a survey by school inspectors to be published today.
The finding will infuriate parents who have been campaigning for more public spending on schools to stop class sizes rising. Polls show that most parents believe that smaller classes mean better education.
However, inspectors from the Office for Standards in Education who compared class size and standards in thousands of lessons found no correlation between the two except in the case of five- to seven-year-olds. Their report says the quality of teaching is paramount.
A marginal decrease in class size of three or four pupils would not improve achievement, the inspectors say. And they produce figures to show that the cost of big reductions would be prohibitive.
Their figures suggest that the Labour Party's costing of its pledge to reduce class sizes to under 30 for five- to seven-year-olds is far too low. The party has promised to pay for its pledge with pounds 60m saved by scrapping the assisted-places scheme.
The inspectors' findings on younger children are supported by the most authoritative research on class size so far, the student-teacher achievement project in Tennessee. It revealed that five-year-olds in classes of 15 did much better in maths and reading than in classes of 24.
The inspectors urge schools to use more classroom assistants to help in larger classes. There are more than 1 million primary school children in classes of more than 30 strong.
Gillian Shephard, the Secretary of State for Education, said last week: "There is no research that formally links marginal differences in class size with the quality of delivery. But clearly huge classes are more difficult to manage."Reuse content