I have extensive experience working with children with autism. Throughout the years, I have learned that it's difficult to evaluate children with autism with limited attending or pre-requisite skills, using standardized tests such as IQ tests.
During a structured testing situation, children should be able to sit for at least 1 consecutive hour without accessing frequent reinforcers. They should be able to follow simple instructions such as show me or do this. They should have enough language to understand what the tester is communicating. Additionally, it is well known that children with autism have difficulty understanding questions which will also be a barrier to completing an IQ test or psycho evaluation.
Children with autism do well-using visuals, they are taught by manipulating pictures, matching items, and pictures, making connections between things using pictures, identifying, and labeling everyday items, opposites, etc. Tests that do not provide the opportunity to manipulate items but just to respond to questions, may eventually not measure children’s IQ but their ability to perform on these types of tests.
I believe that children with autism who do not have the prerequisite skills for completing a structured evaluation should be assessed with instruments that are more relevant to their skills and reality. The typical assessment tools used by behavioral analysts to assess children with limited skills are the VB- MAPP or ABLLS.