Below is a heartbreaking video about a Canadian man diagnosed with Trainable (moderate) Retardation as a child (usually considered IQ 35-40 to 50-55), though he later obtains an IQ of 69, which is the upper end of Educable (mild) Retardation. I think this is a classic example of regression to the mean. The correlation between childhood and adult IQ (measured on the same test) is about 0.73, so someone who scores 45 points below 100 as a kid, might be expected to score only 45(0.73) = 33 points below 100 as an adult (and vice versa), though because the retarded are often segregated (this guy was pulled out of school very young), you might not expect any upward regression, but rather, what Jensen called a cumulative deficit effect, where the IQ of low IQ kids get lower and lower as they get older.
What struck me while watching the video is how normal he seems. His mother seems smart so he doesn’t seem to have familial retardation, yet he has no physical abnormalities, so his retardation doesn’t seem organic either. Perhaps something went wrong prenatally.
He just strikes me as they typical Nova Scotia guy I’d see getting drunk at local bars when I traveled to the Maritimes. In fact he’s more articulate than most. Perhaps his retardation is concentrated in Performance IQ, which would make sense if it was caused by prenatal problems. The only real sign of low IQ is the very small head circumference which I would guess to be 21.5″ around, but that doesn’t seem uncommon in rural Canadian towns.
His girlfriend strikes me as having a towering IQ of 110, probably typical for a Canadian university grad, but well above average for a Canadian college grad (in Canada we separate the two)
He and his girlfriend got an apartment and had kids, but his mother would have none of it, and he was confined to an institution. But he broke free, and started challenging the very law that declared him incompetent.