"Children with autism and Asperger syndrome are 20 times more likely to be excluded from school than their classmates, researchers say.
A report by the National Autistic Society (NAS) says one in five pupils with the conditions are excluded at least once, compared with an estimated 1.2% of the total pupil population.
The researchers found that teachers across the UK frequently have to send home children with autism because schools lack the necessary expertise, time and specialist support.
While nursery schools and primary schools are showing an awareness and ability to respond, the situation deteriorates in the secondary sector, they say. 'Complex condition'
The report, called Inclusion and Autism: Is it Working?, was published on Monday for the launch of Autism Awareness Week.
It says that exclusion of people with autism continues into adulthood, socially and economically.
Only 41% of parents feel their adult child is included in society, and only 2% of adults with autism are in full-time paid work, according to the research.
NAS education advisor Mike Collins said: "Autism is a complex condition, with children having difficulties relating to people and communicating their needs.
"Parents are telling us that everyone involved in the day-to-day running of schools need specific training to recognise and support their children."