Flynn effect reversal began earlier among high-income men, masked by education expansion

Trend reversals in cognitive test scores appeared first among high-income men, with lower-income groups later peaks and smaller declines, in 579,379 Norwegian conscripts. Educational expansion temporarily offset a broader decline, but after plateau, scores fell across all groups.

• Retrospective cohort of 579,379 Norwegian men from 25 birth cohorts (1967–1991) using compulsory military conscription cognitive tests linked to administrative records.
• Socioeconomic differences in test-score trends tracked with educational attainment; after education gains plateaued, declines accelerated across strata, steepest in high-income groups.
• Limitation: male-only, single-country sample; observational design cannot establish causality.

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