The Conversation:  Clinicians make mistakes about intellectual impairments

Intelligence is a difficult thing to measure. While IQ tests have been heavily criticised over the last 30 years, society still sets much store by them. Health and education professionals’ decisions about what placements and interventions are appropriate for disabled children are still informed by the child’s IQ score, for example.

This is paradoxical since if you can’t speak or use your hands, it’s impossible to do these tests. Severely disabled children score very poorly regardless of their ability. Even Stephen Hawking would have been categorised as severely intellectually disabled by this measure.

A growing movement in special education and speech/language therapy has recently been urging practitioners to set aside test scores and “presume competence” in people with severe disabilities – meaning you assume an individual is competent in the absence of good evidence to the contrary. They point to growing signs that the abilities of some children have been grossly underestimated.

Recent developments in Rett syndrome are a case in point. Rett is a severely disabling neurological condition which affects around one in 10,000 girls (and far fewer boys). Several new research papers have found that by testing the intelligence of Rett children in other ways than IQ tests, they turn out to be much more capable than previously believed.

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