There are a variety of reasons, none of them having anything to do with ability, for why an autistic person might do poorly on a standardized test.
In a 2015 blog entry, Kedar describes his experiences with vocabulary drills. He recalls that an evaluator laid out an array of picture flash cards on the table and asked Kedar to point to certain pictures. “My mind might be screaming, ‘Touch tree! Don’t touch house!’ and I would watch, like a spectator, as my hand went to the card my hand, not my brain, wanted,” he writes. “And down in the data book it would be marked that I had not yet mastered the concept of tree.”
Many autistic people similarly say they have poor voluntary control over their movements. A test’s setup, the test taker’s anxiety, or problems with attention can also interfere with the results.
Most IQ tests are administered verbally in a one-on-one setting. That setup may be difficult, if not impossible, for some autistic people because of their social-communication challenges. Restricted interests characteristic of autism can also affect test performance. For instance, if an autistic person is asked to define the word telescope, and astronomy happens to be her special interest, she may talk at length about what she can see through a telescope without ever explaining what a telescope is. “You never get to the point of saying the key elements of the definition I’m looking for, so you may not actually get credit,” Bal says.
Even for tests that can be administered nonverbally, the test taker usually needs to be able to understand or perform complex gestures such as pointing, something else that’s often difficult for people on the spectrum. Many evaluators don’t have the training to help minimally verbal people with autism work around such challenges.
Assessments of cognitive ability also typically take 45 minutes to an hour to complete, too long for autistic people with attention problems and hyperactivity to stay focused. Many lack the motivation to complete the tests in the first place. “You have to motivate them to do the tasks, and the tasks we have that measure cognitive ability are often boring,” says Beth Slomine, a neuropsychologist at the Kennedy Krieger Institute in Baltimore. As a result of all of these factors, she says, “the tasks don’t always measure what we think they’re measuring.”
There is no consensus among experts on which tests are best to use with autistic people, especially those who are minimally verbal. Popular options include the Wechsler Intelligence Scale for Children, the Mullen Scales of Early Learning, the Leiter International Performance Scale, and Raven’s Progressive Matrices, but researchers agree that none is a particularly good fit.
Read: The perils of giving kids IQ tests
There is also confusion over how to interpret the tests’ scores. IQ tests typically calculate an individual’s score by comparing her performance against hundreds, if not thousands, of randomly selected people of about the same age. Most designate the average score as 100, with 95 percent of the population scoring 70 to 130. If an autistic person struggles to complete a test appropriate for her age or scores so low that it’s not plausible, the administrator may try a test designed for a younger age group. This strategy yields an age equivalence rather than a standard score: For example, a 19-year-old man who completes a test for school-age children and receives an age equivalence of 10 has performed similarly to the average score for a representative sample of 10-year-old children. Researchers often divide this age equivalence by chronological age and multiply the result by 100 to yield something called a ratio IQ score.