Thousands of children with autism are being illegally excluded from school, new research suggests.
Youngsters with the condition are being asked to stay at home, miss out on school trips and activities and to come to lessons part-time, according to a report by the Ambitious about Autism charity.
It warns that many children with autism are missing out on education because schools do not have the knowledge and skills to support them.
The report is based on surveys of over 500 families and 1,000 school staff as well as information gathered from local councils.
It found that four in 10 children with autism have been informally excluded from school temporarily - an illegal practice.
Ambitious about Autism said that as around 70,785 children have the condition, this could equate to more than 28,000 illegal exclusions.
Around a fifth (20%) of the parents questioned said that their child with autism has been formally excluded in the last year, while more than half said that they have kept their son or daughter out of school because they were concerned that the school could not provide the right support.
The report also found that two fifths (40%) of parents had been asked to collect their child at an unscheduled time, while three in 10 (30%) said they had been asked by a school to keep their child at home.
It calls for statutory guidance clarifying that schools must tell their local council of any part-time schooling arrangements for children with special educational needs, and their plans to help a child to get back into full-time education.
The charity suggests that schools may be resorting to informal exclusions - which it said can also mean refusing to allow youngsters to take part in social activities or school trips - because they are unable to support youngsters with autism.
While schools do have a legal right to formally exclude a child, this should only be done as a last resort, it argues, and plans should be put in place to ensure the pupil is still getting an education.
The report notes that while over seven in 10 (71%) of autistic children are in mainstream schools, around 60% of teachers in England say they do not feel they have had enough training to teach pupils with the condition.
Jolanta Lasota, chief executive of Ambitious about Autism, said: "It is shocking so many children with autism are missing out on education. All schools are legally bound to provide quality full-time education to all pupils, including children with autism.
"Asking parents to collect their children early or putting them on part-time hours is against the law and fails to address the underlying need for schools to make reasonable adjustments to include children with autism."
She added: "We know schools can and do support children with autism to learn, thrive and achieve. All schools need to build their capacity to support children with autism and not use exclusions as a way of managing their special needs."
The report was published as part of Ambitious about Autism's Ruled Out campaign, which is calling for every school to have access to a specialist autism teacher and to ensure that families with children that have the condition know their rights.
A Department for Education spokeswoman said: "All councils must ensure children are educated in a placement which meets their needs, and we have been clear that schools have a duty to follow our strict rules when excluding pupils.
"We are spending over £3.5 million on Special Educational Needs Co-ordinators in schools to provide targeted support to children with SEN, and have given the National Autistic Society £440,000 to provide advice to parents and teachers about how to support autistic children at school."