The research, published in The Good Schools Guide - Special Educational Needs, supports the growing campaign against the closure of special schools, which are six times less likely to be judged “inadequate” by Ofsted than their mainstream counterparts but three times more likely to be shut.

“There are so many good schools being closed. And yet the special schools are where you see the really innovative teaching,” says Sandra Hutchinson, the guide’s editor.

A third of statemented children in mainstream primaries score up to 3.5 marks less than expected in tests. But for special schools the figure is only 2 per cent, the guide’s researchers, using key stage 2 test data, found. On average, a pupil in a special school achieves 1.5 points more than a similar pupil in a mainstream school.

The worst-performing areas were Slough and Northumberland. A spokeswoman for Slough said the borough admitted a large number of excluded pupils and had a rising immigrant population.

The study, which analysed Year 6 test scores from local authorities across England, will confirm suspicions that special educational needs provision is a postcode lottery.

The proportion of primary school pupils with a statement of special needs ranged from 1 per cent of the total in Nottinghamshire to 7 per cent in Torbay. “We all knew there was a difference, but it seems some authorities are statementing extraordinarily reluctantly and late,” said Mrs Hutchinson.

The number of such children in mainstream education varied from 39 per cent in Poole, Dorset, to 96 per cent in Newham, London.

The guide’s compilers also found that some schools were reluctant to publicise their special needs services.

pound;21,000-a-year Radley College in Oxfordshire responded: “We would rather not appear in any guide of schools offering SEN provision.” Sexey’s School, Somerset, asked for its entry to be deleted.

“It appears many don’t want to be associated with special needs,” said Mrs Hutchinson.

Radley College declined to comment.