Little research has focused on why short-term gains from preschool may disappear and the conditions under which gains from preschool might be sustained into elementary school. We investigate whether two aspects of the elementary school environment may help to sustain the academic gains made during preschool using two random assignment preschool studies: 1) whether advanced and challenging instruction in kindergarten and first grade; 2) professional supports in which preschool teachers interact with their kindergarten and first grade counterparts to coordinate instruction and transition. We also assess whether the child's home learning environment moderates the persistence of preschool effects. We did not find any evidence to support the hypothesis that better instructional quality mitigates the fadeout of preschool treatment effects during elementary school. However, we did find some evidence that when the preschool intervention was coupled with teacher professional supports in kindergarten and first grade, this all but eliminated the fadeout of effects observed between kindergarten and first grade. We also did not find that factors in the home environment, parents education and home learning activities, help to sustain the gains made during preschool. Future research should investigate aligned preschool-elementary school curricular approaches to sustain the benefits of ECE programs for low-income children. (author abstract)