A key government adviser has claimed that schools misdiagnose thousands of children with special educational needs in order to climb the league tables.
Philippa Stobbs said there are "perverse incentives" for teachers to label pupils as having special needs and this then hinders their achievement.
Ms Stobbs, who is a senior SEN adviser to the Department for Children, Schools and Families (DCSF), said "over-labelling" was an example of "laziness" in mainstream schools.
She called for Ofsted and school improvement partners (Sips) to question primaries and secondaries with very high numbers of SEN pupils. In some cases, the proportion reaches almost 50 per cent.
Ms Stobbs likened the situation to leaving children "parked in a lay-by while others motor on past" and said special needs co-ordinators should challenge colleagues who misdiagnose.
"I don't think it's very helpful to infer that children behind in their learning have SEN. They are only working below the standards they should be achieving," she told a conference in London last week.
"There are perverse incentives to have more children on the SEN register. It makes a school's value-added scores look better if you inflate SEN, and there are also funding incentives.
"Teachers need to sidestep the label and look at children's progress in a more responsible way, using their age and prior attainment.
"You can help children progress, you don't need this label, and funding doesn't always depend on the SEN tag. But at the same time, we shouldn't artificially manipulate the number of children who have SEN."
Ms Stobbs, who is the author of SEN guidance for the DCSF, said it was "nonsense" that there were no national standards for statements or the School Action Plus criteria.
Jean Gross, the Government's speech and language "tsar", agreed that misdiagnosis prevents children getting the best-quality education and causes "real" problems as a SEN label often means the pupil works more frequently with a teaching assistant.
A recent government-funded study by London University's Institute of Education found that the more attention pupils receive from support staff, the worse their attainment in core subjects.
But Ms Gross said: "I don't think teachers are being lazy by overdiagnosing - I think it shows they are worried about a child and trying to protect them.
"In primary schools, they are trying to make sure children get help for when they transfer to secondary school. But there are incentives for diagnosing: many local authorities base funding on numbers of children with SEN without moderating those numbers.
"This isn't the fault of the teacher - it's the fault of the system."
But Lynn Greenwold, chief executive of the Professional Association of Teachers of Students with Specific Learning Difficulties, said more children, not fewer, should be diagnosed with SEN.
"Many children have, or are at risk of developing, specific learning difficulties such as dyslexia and this has not been identified.
"In one pupil referral unit all the pupils were in this position," she said.
"Teachers need to know more about the things to look for."
About 117,000 children have special educational needs, and 23,000 have a statement. Only 25 per cent of those with SEN get five good GCSEs, compared with 74 per cent of non-SEN pupils.
In total, 46 schools have 50 per cent or more of pupils classed as SEN; the proportion is between a third and a half in 8 per cent (277) of schools; and a quarter of all pupils in 17 per cent of schools.
Almost a third of Year 5 boys are classed as having SEN.