Children from families with low socioeconomic status (SES) earn lower grades, perform worse on achievement tests, and attain less education on average than their peers from higher-SES families. We evaluated neurocognitive mediators of SES disparities in achievement in a diverse sample of youth whose data were linked to administrative records of performance on school-administered tests of 7th grade reading and math proficiency (N = 203). We used structural equation modeling to evaluate whether associations between SES (measured at ages 8-9) and achievement (measured at age 13) are mediated by verbal ability and executive function (measured at age 10), a suite of top-down mental processes that facilitate control of thinking and behavior. Children from relatively higher-SES families performed better than their lower-SES peers on all neurocognitive and achievement measures, and SES disparities in both reading and math achievement were partially mediated by variation in executive function, but not verbal ability. SES disparities in executive function explained approximately 37% of the SES gap in math achievement and 17% of the SES gap in reading achievement. Exploratory modeling suggests that SES-related variation in working memory may play a particularly prominent role in mediation. We discuss potential implications of these findings for research, intervention programming, and classroom practice.