A substantial body of research points to the persistence of the shape of and variation in educational gradients in cognitive function across the life course, from early adulthood through old age. Fewer studies have considered the roles of educational opportunities and achievements early in the life course in shaping these long-run outcomes. Furthermore, attention has centered on differences in the expectation of cognitive function across levels of education, with relatively less formal consideration of variation in cognitive function within and between levels of educational attainment unaccounted for by educational credentials. We address these gaps in our knowledge, demonstrating that high school educational opportunities, and especially academic achievements, account for most of the variation in cognition across levels of degree attainment on selected HCAP measures in a population representative sample of adults who attended high school in the U.S. in 1980 as they approach 60 years of age.