The sustaining environments hypothesis theorizes that the lasting effects of PreK programs are contingent on the quality of the subsequent learning environment in early elementary school. The current study tests this theory by leveraging data from students (N = 462) who did and did not enroll in the Boston Public Schools (BPS) prekindergarten (PreK) program as well as features of their kindergarten instruction measured at the child- and classroom-levels using surveys and observations. Taken together, findings revealed limited evidence for the sustaining environments hypothesis. The bulk of the results were null, indicating that in general, associations between enrollment in BPS PreK and language, literacy, and math skills through the spring of kindergarten did not vary by kindergarten instructional experiences. When examining distinct types of instructional experiences, there were some inklings that child-level observational measures of kindergarten learning experiences—particularly those capturing constrained versus unconstrained instruction—were more predictive of PreK persistence than observed global classroom quality measures or survey-based measures of advanced instruction. However, these associations were not always specific to outcomes matching the content delivered during this instruction (math vs. literacy), consistent with the possibility of either cross-domain effects or that instructional variables are proxies for more general instructional practices. Findings for future research and theory are discussed. (author abstract)