A controversial policy that presumes all pupils should be taught in mainstream schools regardless of how vulnerable they are should be urgently reviewed, teachers and charities have said.

The call comes after a series of reports raising major concerns over the way pupils with complex learning or behavioural difficulties are being supported at school.

Since 2003 there has been a legally-enforceable “presumption of mainstreaming” to integrate children with additional support needs (ASN) into primary and secondary schools.

However, while mainstreaming has widespread support in principle it has been the focus of increasing concern from families and education staff because of a lack of resources.

Charlene Tait, deputy chief executive at Autism Scotland said because of the policy lots of pupils were being sent to mainstream schools "almost regardless" and even if parents knew it was not the right setting for them.

She said: "There needs to be more flexibility in terms of the policy and it should not be the assumption that children who have been at three, four or five mainstream schools should continue to be sent to mainstream school.

"You are being put into the same model every time and you might strike it lucky and get a teacher who can teach and support you well, but it is still in a context where the pupil is in an environment that they find difficult to manage.

"The presumption of mainstreaming is a really laudable policy and one that we are all in support of, but there are some children that just cannot access education in that way and it is not going to happen by wishful thinking. It needs resources, a specific approach to training and an understanding of how autistic people think because the experience in some of these school environments is overwhelming."

Kenny Graham from Falkland House School, a member of the Scottish Children’s Services Coalition, a group of private and charitable organisations who work with vulnerable children, called for more resources.

He said: "The key is to adopt a child-focused approach in which the needs of the individual are addressed. A mainstream environment, while perceived as ideal, may not be suitable for all.

"The focus should be on ensuring that children get the right support in the right location, regardless of whether that is a mainstream or a specialist setting."

Larry Flanagan, general secretary of the Educational Institute of Scotland, said issues were being exacerbated because there had been an increase in the number of ASN pupils at a time when specialist teachers were reducing.

He said: "Schools are struggling to cope with pupils in a situation where they are not being supported properly and it is disrupting teaching for other pupils.

"There needs to be a major review of how ASN pupils are being supported because it is now a significant challenge for the education system with kids in difficulty who are not being supported."

Seamus Searson, general secretary of the Scottish Secondary Teachers' Association also called for a fundamental review of the policy.

He said: "The assumption that mainstream is best can be the right one, but it is not necessarily the case because schools don't have the resources to make sure every youngster is supported in the way they should be.

"There are a lot of pupils in mainstream schools that would benefit from extra support, but there isn't enough time to assess them properly and the support often isn't available anyway.

"Shortchanging these youngsters in unfair because, without the support they need, they are wasting their time and they get frustrated and upset and rightly so."

In December almost 3,000 people signed a letter calling for John Swinney, the Education Secretary, to address the barriers autistic children face to accessing education.

The letter, backed by Children in Scotland, the National Autistic Society Scotland and Scottish Autism, followed a survey of nearly 1,500 parents which raised significant concerns over the ability of schools to cope.

More than one third of parents said their child had been unlawfully excluded in the last two years with 22 per cent saying it had happened multiple times a week.

In December an investigation by Scotland’s Children’s Commissioner found challenging pupils were being routinely restrained or locked up in classrooms.

Mr Swinney said: "I am absolutely committed to the principle of mainstreaming, but the principle is underpinned by ensuring the correct support is available and the correct assumption is made about the educational setting in which a young person can be educated.

"What I am looking at is how to ensure that is the case across the country and I will reflect on these issues as part of assessing the guidance on this issue.

"We have to be certain that a young person is in the right educational setting. In some circumstances that will be possible and practical to do and in others it won't and it is essential that we consider carefully each of those cases. I want to make sure I am able to fulfil the principle that underpins mainstreaming."

A Scottish Government's consultation on the guidance on mainstreaming published in June highlighted a raft of associated problems including violence and disruption due to lack of support staff.

One teacher said: “The damage being done is terrifying and our children are being let down by us regardless of how hard we try in class.”