Genetic studies show that children's reading achievement is in part genetically influenced, and intervention studies show that reading achievement can be increased by environmental interventions. However, correlational and mean-level analytic strategies are rarely integrated into achievement research, potentially leading to misinterpretation of results. The parent-offspring adoption design offers a novel opportunity to examine the independent and joint roles of genetic and rearing environmental contributions. The sample included 344 adopted children in first grade and their biological and adoptive parents. Results indicated that adoptees' reading scores were correlated with their biological parents' scores, but not with their adoptive parents' scores, suggesting genetic influences. In addition, examination of mean scores indicated that adoptees' scores were significantly greater than their biological parents' (p's < 0.001) for all subtests, suggesting promotive effects of the rearing environment. This pattern was present even when biological parents scored >1 standard deviation below the biological parent mean on achievement.