Autism "affects 6,000 children and young people in Wales"
Educational institutions in Wales are "not meeting the needs" of young people with autism, a study suggests.
A report by the Welsh assembly's cross-party autism group (CPAG) revealed 75% of schools surveyed felt there was a lack of adequate local help available.
Some 58% described further education provision in Wales as inadequate.
The National Autistic Society Cymru said the absence of support for autistic young people and their families was "sometimes devastating".
The study, A Snapshot of Autism Education Provision in Wales, is based on information gathered from 33 education providers.
These include special schools, mainstream schools with autism resources and further education (FE) colleges.
It follows concerns raised in a number of CPAG meetings that young people with autism in post-16 and further education were missing out due to a lack of organisation, awareness and understanding.
The report examines topics such as the role of the Welsh Assembly Government's strategic action plan on autistic spectrum disorders, released last year.
It also looks at cooperation between local agencies, schools and colleges and disparities between state and independent provision.
The report also looks specifically at issues affecting young people with Asperger's syndrome, a condition on the 'higher end' of the autism spectrum.
As one parent told the CPAG: "My son will be leaving education soon. We are having to look for a college in England.
"There is nothing suitable in south Wales for him to go to (post-16) so we are having to look in England for places that aren't too far away."
75% of schools feel that there is a lack of adequate local provision of services for the young people they support.
57% of state schools feel out-competed by the independent sector.
58% said there is inadequate FE provision for young people on the autism spectrum in Wales.
75% of schools think there are specific issues for young people with Asperger's syndrome in accessing ongoing support in college.
Source: A Snapshot of Autism Education Provision in Wales
Commenting on the report, Janet Ryder, assembly member and CPAG chair, said the report offered "a useful insight into the problems faced by young people with autism in Wales, as well as problems faced by the education providers themselves".
"Some cases of good practice have also been highlighted, which we hope will serve as examples elsewhere in Wales," she added.
"In many cases, if these institutions have an improved understanding an awareness of autism, coupled with suitable guidance, the problems young people face can be addressed."
Shirley Parsley, national coordinator of the National Autistic Society Cymru, said the issues highlighted in the report were daily realities for young people with autism and their families in Wales.
She said: "We are told of parents who have had under a week between hearing a decision on a placement, and their child beginning college.
"Autism is much more common than most people think. It affects over 25,000 people in Wales. Of these, 6,000 are children and young people aged under 18.
"Missing out on the right support at the right time can have a profound - sometimes devastating - effect on these youngsters and their families."
CPAG was established in 2002 to bring individuals, families, professionals and AMs together to discuss autism issues.
The report is being launched at an event hosted by the CPAG at the Senedd Building, Cardiff Bay.