Thanks Perz, You are generous soul..........

Wikipedia gives a pretty good description of HFA: http://en.wikipedia.org/wiki/High-functioning_autism

The wiki article stresses that HFA is an informal term. The DSM-IV criteria for autism does not differentiate HFA and does not break down the autism spectrum into "levels of functioning." Asperger's, which is often thought of as a milder form of autism" is compared with autism in the DSM, but only in terms of the person not having any "signiificant delays or deviances in language acquisition." A child with Asperger's may exhibit as many or even more symptoms in the other two areas (social interractiona and repetitive behaviors) as a child diagnosed with autism. There are many websites that list the DSM-IV criteria for autism and I have previously posted several different links in other comments. The one here is from the Geneva Centre for Autism in Toronto: http://www.autism.net/content/view/195/93/ (please note that it continues over 3 pages on this website). Wikipedia has a general discussion on the DSM which sheds some light on how that particular manual is used by the psychiatric profession and how it is regarded: http://en.wikipedia.org/wiki/DSM-IV-TR

There does seem to be a need to break down the autism spectrum into levels of functioning when decisions are being made as to what services the child requires. For better or worse (and probably for the worse), our whole education system is based on "grading" children according to differing levels of ability. For example, it is impractical and undesireable to shadow every child diagnosed with autism or Aspergers with a paraprofessional since doing so costs too much money and it can impede some children from attaining the highest level of independence they might be capable of. The reality is that some children with Aspergers may require such services and others may not and some children with autism may and others with autism may not.

So perhaps it was inevitable that CARS was developed as an enhancement to the DSM-IV. CARS stands for Childhood Autism Rating Scale and it does differentiate on the basis of level of functioning. I believe the term HFA may have come about as a result of the use of this scale as a diagnostic tool. There is a Wikipedia article on CARS at http://en.wikipedia.org/wiki/Childhood_Autism_Rating_Scale

Hope this helps,
Perz