We’ve been told since the 1980s that IQ scores are incredibly sensitive to the environment, as proven by the fact that scores have been increasing at a rate of 3 points per decade since the earliest days of testing, and the tests must constantly be renormed to keep the average at 100.

However I’ve always suspected that the Flynn effect was an exaggeration and have been quietly collecting evidence to prove it. Most recently, I found a 1961 paper by Betsy Worth Estes et al., in which 82 kids (grades one through eight) who had taken the 1937 Stanford Binet were tested on the 1960 version. Given the Flynn effect is supposedly 3 points a decade, you’d expect them to score 6.9 points higher on the older test, than on the newer one, but instead the gap was only 2 points (IQ 125 on the 1937 S-B, IQ 123 on the 1960 S-B),

From Relationships between 1960 Stanford-Binet, 1937 Stanford-Binet, WISC, Raven and Draw-a-Man by Betsy Worth Estes et al,, 1961