Beyond years of schooling: Shifting genetic influences across educational milestones in two Norwegian cohorts

Although educational attainment is heritable, its conventional measurement in genetic research as years of education (EduYears) is not designed to reveal potential stage-specific genetic influences across discrete milestones. In two Norwegian cohorts (Norwegian Mother, Father and Child Cohort Study, N = 120,527; Norwegian Twin Registry, N = 8,910), we quantified the genetic contributions to completing high school, bachelors, masters and PhD using genome-wide association studies (GWAS), polygenic indices (PGIs) and twin models. Transition-specific analyses, conditioning on prior success, revealed that observed-scale common-variant heritability (h2SNP) and PGI predictability followed an inverse-U pattern, peaking at the transition into higher education (h2SNP {approx} 0.14; R2Tjur {approx} 0.05) before declining for postgraduate degrees. Genetic correlations (rg) with large-scale GWAS of EduYears (EA4) and intelligence (IQ3) were high for early transitions but declined markedly for later ones (e.g., rg with EA4 from {approx} 0.92 to {approx} 0.38). In cumulative analyses, aggregating liability across prior milestones, the gap between twin- and SNP-based heritability narrowed at higher levels of attainment (h2twin {approx} 0.6[->]0.3; h2SNP {approx} 0.22[->]0.19), while the genetic overlap between distant milestones diminished (rg {approx} 0.92[->]0.71). These patterns, obscured by EduYears metrics, highlight a dynamic genetic architecture across educational milestones, refining polygenic prediction and addressing misconceptions about uniform genetic influences on educational progression.