Nothing, it seems, had changed. Those facts, however, disguise a surprising truth. IQ tests are based on scaled scores. That is: the student’s raw test score is translated into an IQ score according to a formula. And — here’s the key part — that formula is readjusted every ten years. So: the reason that average IQ scores haven’t changed is that the formula has changed to keep the average at 100. A lot. Raw scores on the underlying test have gone considerably over the history over the test. If our grandparents’ raw scores were translated according to today’s formula, their average would be about 70. If our scores were translated according to our grandparents’ formula, the average would be about 130.