School achievement strongly predicts midlife IQ

The relationship between measures of IQ and standardized school achievement tests is well established at around r ≈ 0.5 when the two are measured in close proximity. The current paper examined the stability of this correlation when comparing elementary school achievement (grades 3–8) and midlife IQ. Iowa Adoption Study participants who had standardized school achievement measures (ITBS) on file were given the WAIS-III. Mean age at IQ testing was 44.01 years (SD 6.65 years). The correlation between school achievement and WAIS-III FSIQ was r = 0.64, suggesting substantial life span stability in this relationship. Furthermore, elementary school achievement was substantially correlated with occupational status and household income at midlife. These findings suggest that standardized school achievement data is a useful measure of premorbid IQ.