I've not read this book but I have read plenty of other material by Thomas Sowell. He is a very intelligent man, but this is a personal subject for him. His son was a very late talker and went on to be an engineer and a very "normal", "successful" person. I suspect if we met this young man, we would identify some aspie traits in him.
I do not believe that Sowell is arguing that these children should be held to super high expectations or diagnosed with something called "Einstein Syndrome". I think his point is that we have too many labels, that "spectrum" labels are inappropriate, and that such labels aren't always a good idea.
Sowell essentially argues that many children who are labeled "autistic" are actually not. They may develop at different rates or in different ways, but they grow up perfectly able to funtion in society. To an extent I agree, but I think it's also fairly obvious by now that both low and high functioning autism have a genetic link. Right here on this forum we have a lot of HFAs who have LFA children. I don't think we can say that these conditions are totally different, even though the HFA holds a job and may even be able to present himself as NT.
I do see his point though. If my own son had been tested at 18 months, he would have been found to be quite severely autistic. He had long screaming fits (hours), spent all his time lining up toys and stimming, would look nobody in the eye, had many sensory issues, lost all language, was behind in most develomental goals, etc. However, by the time he had undergone six months of therapy and finally saw a developmental pediatrician at age two, he showed no clinically significant signs of autism and was developmentally advanced in all categories. Does he have autistic traits? Yes. Will anybody diagnose him? No--he's just not that severe. He's a bright boy with an unusual brain that happened to develop in spurts rather than gradually like most children. I really don't even know whether early intervention therapies helped, or whether it was just time for him to achieve that growth.
Here is an article by Sowell: Testing, Testing: Intervening Dangers
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The machine does not isolate man from the great problems of nature but plunges him more deeply into them. -Antoine de Saint Exupéry