Mediators of IQ score differences of Whites with Hispanics and African Americans are reviewed in the WISC-IV, WISC-V, and WAIS-IV. Mediators included parent education, income and academic expectations for children and adolescents, and self-education, income and occupation for adults. Results showed that these variables account for substantial portions of variance in all group comparisons, but least for African Americans and adults. The critical influence of cognitively enriching and impoverishing environments on the neurocognitive development of children, and the unequal distribution of these influences across social and economic groups are discussed as complementary with interpretations of acculturation and heredity.