Each year of schooling raises a child’s IQ, writes Catherine Johnson on Kitchen Table Math. She quotes a researcher on a review of over 50 studes:
These studies, conducted throughout the 20th century, comparing schooled and non-schooled populations, have estimated that the enhancement of IQ by schooling ranges from 0.3 to 0.6 of an IQ point for every year of school competed. Importantly, the association between IQ and exposure to formal education is not only due to children with higher measured IQ staying in school longer.”
I know there’s been a steady increase in IQ over the last century as education has expanded.