This study examined shared environmental influences on the longitudinal stability of general cognitive ability, as mediated by socioeconomic status and chaos in the home, using 287 pairs of elementary school-age twins drawn from the Western Reserve Reading Project (WRRP). General cognitive ability was evaluated at two annual assessments using the Stanford-Binet Intelligence Test. SES was examined using the highest level of education achieved by the mother of the twins, and chaos by a 6-item parent-report questionnaire. Results suggest that SES and CHAOS not only account for independent sources of shared environmental influences related to general cognitive ability at a given measurement occasion, but these effects also account for a portion of the longitudinal stability of general cognitive ability in early childhood.