Prior research shows that short-term effects from preschool may disappear, but little research has considered which environmental conditions might sustain academic advantages from preschool into elementary school. Using secondary data from two preschool experiments, we investigate whether features of elementary schools, particularly advanced content and high-quality instruction in kindergarten and first grade, as well as professional supports to coordinate curricular instruction, reduce fadeout. Across both studies, our measures of instruction did not moderate fadeout. However, results indicated that targeted teacher professional supports substantially mitigated fadeout between kindergarten and first grade but that this was not mediated through classroom quality. Future research should investigate the specific mechanisms through which aligned preschool-elementary school curricular approaches can sustain the benefits of preschool programs for low-income children. [This paper was published in the "Journal of Research on Educational Effectiveness" v11 n3 p339-374 2018 (EJ1181585).]