Prior research shows that short-term treatment effects from preschool may disappear, but little research has considered which environmental conditions might sustain the academic advantages from preschool into elementary school. Using two random-assignment studies, we investigate whether two features of the elementary school environment help to sustain preschool academic gains: 1) exposure to advanced and high-quality instruction in kindergarten and first grade; 2) professional supports to coordinate curricular instruction and transition. Across both studies, our measures of instruction did not moderate fadeout from preschool. However, results indicated that targeted teacher professional supports substantially mitigated fadeout between kindergarten and first grade. Future research should investigate whether aligned preschool-elementary school curricular approaches can sustain the benefits of preschool programs for low-income children. (author abstract)