Baroness Mary Warnock once described the definition of special educational needs (SEN) as “the purest vicious circle you will ever know”.

“A special need is defined as ‘any need that the school needs to take special measures to meet’,” said the peer, who was honoured again in the New Year’s list last year for her services to children with SEN.

“I think it is that vagueness actually which has led to… the very bad habit of talking of SEN children as a class, a category, of children, all of whom would be expected to flourish in the same sort of environment.”

More than a decade has passed since Baroness Warnock gave this evidence to a parliamentary committee, but pupils with special education needs and disability (SEND) are still caught in a “vicious circle” when it comes to catering for their needs.

Data from 90 English local authorities collated by Tes shows their annual fees for sending such children to private special schools surged by 40 per cent between 2012-13 and 2017-18 to more than £565 million pounds.

Much of the increase can be explained by the extra 30,000 children with a SEN statement or Education Health and Care (EHC) plan which entered the education system between 2012-13 and 2017-18.

Faced with a long-term budget squeeze, the argument goes, local authorities are outsourcing these pupils to independent providers which can offer more specialist services than mainstream schools.

While this may be true, experts said there are also other complex factors at work.

Dr Artemi Sakellariadi, the director of the Centre for Studies on Inclusive Education (CSIE), argues the shift has been driven by the constant pressure on schools to produce top-notch exam results.

“Some children will never get their English and maths GCSEs but that doesn’t mean they are a failure,” she said. “Our school workforce is put under intense pressure and one of the responses, I think, is to say this child needs specialist help.”

Professor Brahm Norwich, an expert in SEN from the University of Exeter, said public data shows academies, in particular, have reduced the number of pupils with SEN on their books since 2011.

Because schools named in an ECH plan must legally take that pupil, this is often done “subtly” he said, adding: “There are ways in which you put pressures and create what is called an intolerant environment.”

He gave the example of one school which forced an autistic boy to wear a tie he hated to the point where the pupil was so stressed he could no longer bear to attend classes.

Lizzie Harris, deputy head of an academy in Newham, London, which has a reputation as one of the most inclusive authorities in the country, said some schools “go out of their way” to make parents of SEN children feel unwanted.

“If you walk around a school and you do not think your child is welcome, you are unlikely to send your child there,” she wrote in a recent report.

The Children and Families Act 2014 has made parents’ feelings an increasingly important factor in SEN provision by giving them more say in which school their child will attend.

Maria Bloom, from the legal team at Independent Parental Special Education Advice (IPSEA), said most parents only choose private special schools “reluctantly,” often after painful experiences with mainstream education.

Many of the children IPSEA helps are on the autistic spectrum and find themselves “overwhelmed” when they move from small primary schools to larger secondaries, she said.

“It’s not an easy battle for parents to win,” she explained. “These specialist independent schools often require long journeys… it’s not an easy option.”

Claire Dorer, chief executive of the National Association of Independent Schools and Non-Maintained Special Schools (NASS), agreed, saying her members are providing for a growing number of pupils with complex learning and mental health issues.

She pointed to a NASS survey which found that 60 per cent of parents had tried at least two other schools before placing their child with a private special school, and 20 per cent had tried at least four.

“It is rarely the case that an independent school is the first placement of choice,” she said. “It is usually a result of, potentially, needs not having been addressed earlier.”

The growing number of children with far more complex SEN means independent special schools are now facing their own budgetary squeeze.

The local authority data collated by Tes show that while overall spending on private special schools increased between 2012-13 and 2017-18, the average cost per pupil fell slightly from £45,805 to £45,166.

Colin Horswell, managing director of public service consultancy Cordis Bright, said the reduction is due to pressure from local authorities, cuts in services and therapies, and consolidation of special schools in some parts of the country.

It could also “be the result of commissioners developing hybrid models that support children closer to home and reduce the demand for 52-week residential places,” as is happening with looked-after children, he added.

Increasingly, it seems, schools and authorities alike are being forced to recognise that pupils with SEND are not “a class, a category, of children, all of whom would be expected to flourish in the same sort of environment”.

Times may have changed, but the “vicious circle” of SEND still seems to ring true.