We engage the concept of ecological instability to assess whether children's exposure to frequent change in multiple contexts is associated with teacher reports of students' overall behavior, externalizing behavior, and approach to learning during kindergarten. We operationalize multiple dimensions of children's exposure to repeated change-including the frequency, concurrency, chronicity, timing, and types of changes children experience-in a nationally representative longitudinal cohort of U.S.-born children (Early Childhood Longitudinal Study-Birth Cohort, N ~ 4,750). We focus on early childhood, a period of substantial flux in children's family and neighborhood contexts. Predicted behavior scores differ by approximately one-fifth of a standard deviation for children who experienced high or chronic exposure to ecological change compared with those who experienced little or no change. These findings emphasize the distinctiveness of multidomain ecological instability as a risk factor for healthy development that should be conceptualized differently from the broader concept of normative levels of change in early childhood environments.