Direct and indirect genetic effects on educational achievement vary across countries and ages

Polygenic score (PGS) predictions of educational achievement are sizeable at population level. They capture so-called ‘direct’ genetic effects that are independent of environmental confounding, but also ‘indirect’ genetic effects due to gene-environment correlations, assortative mating, and population stratification. Indirect genetic effects complicate the interpretation and application of PGS predictions. Here, we systematically charted the variability of PGS predictions in N=8,115 dizygotic twins from UK, US, Swedish, and German samples aged 7 to 19 years. Population-level PGS predictions of educational achievement ranged from beta =.16 to .37 across ages and countries. Indirect genetic effects due to environmental confounding accounted for 10% to 65% of the population-level PGS predictions, with family socioeconomic status explaining 29-100% of these indirect genetic effects. Variability in direct and indirect genetic effects was largely unsystematic across countries’ school systems (multi-tiered vs. comprehensive) and children’s ages. Therefore, interpretations of indirect genetic effects on educational achievement remain, at present, speculative.