Can this effect be explained by the fact that since the invention of the test, much of our education was directed toward getting children to have better and better scores in such tests?

BTW. as flynn said:

"The hypothesis that best fits the results is that IQ tests do not measure intelligence but rather correlate with a weak causal link to intelligence."

Which means that much of your article - which depends on the validity of IQ tests - is dubious.

Perhaps what you consider to be "education independed" - finding connections between words and shapes isn't so independed?