By looking at a reform which increased mandatory schooling and prevented people from dropping out of school after the 7th grade, it is fairly certain that the effects seen are an effect of schooling on IQ, not vice versa, she explained.
"One subtle point of our findings is that we use IQ measures at roughly age 19, which is three to four years after the additional education generally was received. Thus, we are not simply picking up a short-lived effect that peters out shortly after people leave school," Galloway said.
The findings suggest that education as late as the middle teenage years may have a sizeable effect on IQ, but do not challenge the well-documented importance of early childhood experiences on cognitive development, according to the authors.
Robert Sternberg, a professor of psychology and provost at Oklahoma State University in Stillwater, said that "these results -- that schooling has a substantial effect on IQ -- replicate those of other, perhaps not quite as well-controlled, studies."
"I am aware of no serious studies that show the opposite result," he added.
He said the results are also consistent with the huge literature on the so-called Flynn effect showing that IQs are modifiable across as well as within generations and have been rising since the beginning of the 20th century.
"The results of this study are problematical for the chorus of psychologists and educators still locked in century-old thinking that IQ is genetic, stable and non-modifiable," Sternberg said. "As, for these individuals, the belief in the stability of IQ is more a matter of re
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