I don’t disagree with what you’re saying, but the concept that environment, including educational environment, significantly affects IQ scores is contrary to the notion, popular with some FReepers, that IQ is set in stone at birth and that large swathes of the population are inherently incapable of learning to read and do basic math.
Someone ... maybe the Thernstroms, or Thomas Sowell ... wrote about a study which showed that IQ in elementary-school age correlates closely with the child’s aural vocabulary - the number of spoke words he understands - at age 5. The writer pointed out that talking to and reading to a young child is a very low-cost, high-return intervention.
It’s well known that IQ can change throughout one’s life, dependent upon diet, environment, stimulation. There was one case in New York where an accused murderer, a young black male, had a measured IQ in the high 60’s. Fortunately for him, New York will not apply a death penalty if an accused’s IQ has measured below 75 because of the issue of competence. However, over time, the accused was spending time with his lawyers, and hearing big words and complex explanations. When they retested him later on, before the trial, his time with his lawyers pushed his IQ above the threshold, allowing the prosecution to make it a death penalty case.
Whoops. :)