IQ tests measure one type of cognitive ability. If English is your second language, or if you school didn't stress basic logic and math you test lower.
But with better nutrition and less social neglect, IQ is actually going up world wide
But drug and alcohol use in pregnant women lowers IQ.
Finally, it depends who you test. Children with mental retardation and autism who in the past would not be in schools and therefore not tested are now living at home and go to public schools.
Now if you want to argue the schools are terrible and don't do basic teaching, well then I won't argue.
But this argument comes from Europe, where the eugenic ideas are still strong, so I am not sure I trust it.
Again, in 1911 (when eugenics was popular) the British argued the Irish were inferior because of their low IQ testing..and in the US, the argument was that Jewish immigrants had an average IQ of 80 and they were considered inferior too.
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