ScienceNOW Daily News has an article on The Case of Mistaken IQ:
Health workers routinely assess autistics using a standard IQ test known as the Wechsler test. But this test requires that children understand oral commands, a trait that many autistic children have trouble with. Cognitive neuroscientist Laurent Mottron of the Hopital Riviere-des-Prairies, Montreal and colleagues noticed that autistic children did poorly on the verbal comprehension part of the Wechsler but exceedingly well on a part that tests non-verbal intelligence and reasoning.
So the researchers decided to test 30 autistic children and 30 autistic adults with a different IQ test called the Raven’s Progressive Matrices test, which is written rather than oral. Healthy children and adults performed similarly on both the Wechsler and the Raven test. But speaking autistics scored up to 30 percentile points higher on the Raven test than the Wechsler test, the researchers reported here 19 February at the annual meeting for the American Association for the Advancement of Science (which publishes ScienceNOW). “Thirty percentile points could raise a retarded person to normal or a normal one to a superintelligent one,” says Mottron.
It sounds like a bit of factor analysis could have gotten them the same result. I didn’t find an actual reference, but here’s the AAAS press release about the symposium.