The number of children with recognised special educational needs attending special schools has risen in recent years, as has the quality of provision.
More children with Education, Health and Care plans or statements are now educated within maintained special schools than at any point since 2007, with 43 per cent going into maintained provision as of January 2016, data from the Department of Education shows.
Meanwhile, the proportion of these pupils placed in independent schools increased from just under four per cent in 2009 to above six per cent in 2016, with an additional two per cent entering non-maintained special schools - a specific type of independent provider.
Ofsted's 2016 annual report says evidence from local area inspections suggests the rise in the proportion of special school placements may relate to parents' concerns of perceived or real inconsistencies in awareness among staff in maintained schools on the support children need.
It adds: "Parents have also raised concerns about the ability of mainstream schools to deliver specialist support, such as therapy, which is readily available in special schools."
Parents' lack of confidence in mainstream provision means most council-maintained special schools are "full to bursting", according to Claire Dorer, chief executive of the National Association of Independent and Non-maintained Special Schools. "Local authorities have little choice but to place more children in the independent and non-maintained sector while they look to set up special free schools to reduce pressure on their own schools," she adds.
According to Ofsted's report, there were 1,038 maintained special schools as of 2016. Of these, 81 per cent - 836 - were local authority-run. In addition, there were 150 special academy convertors, 33 sponsor-led special academies and 19 special free schools. The report also shows there were 441 non-association independent special schools.
Ofsted inspection results suggest the quality of provision tends to be better in state schools, including both maintained special schools and free schools and academies, with only seven per cent judged less than "good". Less than good provision is more widespread in non-association independent special schools at 23 per cent (see graphic).
The characteristics of highly effective special schools - whether independent or maintained - do not differ from mainstream schools, says Ofsted's annual report.
"In the most effective special schools, we see leaders who are clear about their duties and responsibilities in meeting their pupils' identified special educational needs," says the report. "They also deliver a broad, rich curriculum that helps each pupil be ready for their next steps in education and life."
The best schools provide an "enabling" curriculum "rather than a disabling one" and check rigorously on pupils' progress in technical and vocational knowledge and skills, as well as specialist areas such as mobility, independence, communication and behaviour management (see case study). By contrast, in schools rated less than good, children are often not challenged, with limitations "taken as read".
Some special schools are residential schools with wide variations in size and nature. "The sector ranges from large non-maintained special schools which make provision for very specific needs and take children as full boarders from all over the country, to smaller more local providers catering for children with a range of different special needs and disabilities who may be resident at the school only during the week," says Ofsted.
Some residential special schools - with children in residence for more than 295 days a year - are registered as children's homes.
There are also a small number of independent residential special schools that cater for children with very specialist needs.
A total of 57 residential special schools registered as children's homes were inspected in the six months from 1 April to 30 September 2016.
Compared to the 1,126 standard children's homes and 13 secure children's homes inspected during the same period, residential special schools registered as children's homes had the poorest inspection results, with only 63 per cent achieving a good or better judgment. This compares to 73 per cent of children's homes and 77 per cent of secure children's homes.
The exact number of residential special schools is not clear due to different registration requirements. Dame Christine Lenehan's review of residential special schools and colleges - due to report in the autumn - is aware of 330 establishments and estimates 5,000 children and young people are cared for in such provision.
As well as providing a clearer picture of the pattern of provision, the review will look at the quality of services, experiences and outcomes of children, and how these can be improved.
One issue that has arisen from other studies is the use of restraint on children with SEN and disabilities. Earlier this year a BBC investigation - based on Freedom of Information requests to local authorities in England, Scotland and Wales - revealed 13,000 incidents of physical restraint in special schools in the past three years, resulting in 731 injuries.
However, less than one-fifth of authorities were able to provide data - with most saying they did not record such information.
At the time, the Department for Education said it planned to publish draft guidelines on reducing the need for restraint in special schools.
Staff prove the ‘backbone' to success
Perseid School, London | Outstanding | December 2015
Perseid School in the London Borough of Merton is a maintained special school catering for children and young people aged three to 19 with severe and profound learning disabilities.
It has consistently been rated "outstanding" by Ofsted and was described as a "happy and inspirational" place after its most recent inspection visit in December 2015.
Key to the setting's success is its investment in staff, explains long-standing head teacher Tina Harvey. "In any school, the staff team are the backbone and so the starting point is making sure you make the right appointments whether that is teachers, teaching assistants or back office staff," she says.
The school actively targets newly qualified teachers who embark on a comprehensive induction programme, which includes accredited or certified training in all the different communication approaches used by the school and the National Autistic Society's TEACCH training course designed to boost understanding of working with people on the autism spectrum.
By offering a bespoke programme of continuing professional development, the schools aims to attract and retain the best people. For teachers, this can include funding post-graduate studies and leadership development.
"You can appoint the right people, but then you have to support them to unlock their potential," says Harvey.
"We have tried to create a pathway that means teachers want to stay with us. So we might fund them for a post-graduate one-year course or a Masters and hope that hooks them in and means they want to carry on working with us."
The school, which has 25 teachers and 85 to 90 support staff, also provides a comprehensive in-house training programme for teaching assistants.
All staff are encouraged to take on new roles and responsibilities, and develop their skills. Regular coaching is a key part of staff development, with monthly supervision or coaching meetings for all the school's senior leaders and half-termly coaching or supervision for middle leaders.
Another key to success is "the importance of being absolutely clear what your vision and purpose is", says Harvey.
"Initiatives are rolled out so fast that sometimes you feel there is no time to embed or consolidate and there is a risk the school could lose its way a bit due to initiative overload," she says.
"We have come to understand that it is absolutely vital that we decide ourselves what we stand for - what initiatives we want to adopt and the initiatives we're not going to be running with."
The school's slogan is "blazing a trail" and this means constantly looking ahead to identify best practice. "We're ambitious for our pupils and in order to realise that ambition we need to blaze a trail with our approaches," she says. "We' are always looking ahead to see what more we can do and are constantly challenges ourselves."
The school is at the heart of a teaching alliance and Harvey emphasises the importance of being an "outward-facing school with strong partnerships".
Its outstanding rating has given the school more freedom to innovate, including looking at methods of assessment.
"We have been able to look more closely at a holistic assessment approach - linking education goals and therapy goals in a way that perhaps wasn't recognised as so valuable under previous regimes," says Harvey.