Thousands of children with autism are being illegally excluded from schools in England, a charity claims.
In a survey of 500 families, Ambitious about Autism found four in 10 children had been informally excluded from school temporarily, which is illegal.
The charity said children with autism were being asked to stay at home, miss school trips and activities and to attend lessons on a part-time basis.
The government said schools had to follow strict rules over exclusions.
The report is based on surveys of 500 families with a child with autism and 1,000 school staff. It also drew on information from local councils.
Ambitious about Autism found one-fifth (20%) of the parents questioned said their child had been formally excluded in the past year, while almost four in 10 children (39%) had been subject to informal exclusions.
The charity said that as about 71,00 children have the condition, it could mean more than 28,000 children were subject to illegal exclusions across England.
Schools in England must follow procedures set out by the Department for Education when excluding pupils, for example, a head teacher must notify parents of the period of the exclusion and the reasons for it.
Unscheduled pick-up
More than half said that they had kept their son or daughter out of school because they were concerned that the school was not able to provide the right support.
The report also found that two-fifths of parents had been asked to collect their child at an unscheduled time, while three in 10 said they had been asked by a school to keep their child at home.
Ambitious about Autism suggests that schools may be resorting to informal exclusions - which could 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 have a legal right to formally exclude a child, this should be done only as a last resort, it argues, and plans should be put in place to ensure the pupil is still getting an education.
One parent, Clare Moore, said: "I have lost count of the number of times different schools have rung and asked me to collect my son early or keep him at home because they could not support his needs.
"It has been really distressing for him because it interrupted his routine and he never knew how long he would be in school for each day.
"It has also had a massive impact on our family life because I had to give up work as I had to be available at short notice."
'Shocking'
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 said, while many schools do support children with autism to learn, all needed to build on their capacity to do so.
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 £3.5m on SEN 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."
