Sleep has clear importance for academic success. However, most research in this area has focused on older children and adolescents and has used narrow measures of academic achievement, overlooking the importance of early sleep problems in shaping children's classroom behaviors that support academic success. Using a community sample (N = 276, 50% female), the current study examined associations between parent-reported preschool sleep problems (Mage = 3.84, SD = 0.83) and three dimensions of classroom engagement coded during live classroom observations in the first grade (Mage = 6.72, SD = 0.34). The moderating role of family socioeconomic status (SES) was also considered. A multivariate multilevel model found that more preschool sleep problems were associated with less focused engagement (defined as involvement in academic tasks, such as writing or asking questions), but more competing responses (defined as inappropriate or distracting behaviors). Preschool sleep problems were not associated with task management (defined as preparation for academic tasks, such as locating classroom materials). Although family SES did not moderate any of these associations, higher income-to-needs ratios in preschool were associated with more focused engagement and fewer competing responses. Findings highlight the role of early sleep problems in classroom behaviors that facilitate academic success. Targeting sleep problems prior to the school transition may serve as a useful approach to optimizing learning conditions during this key developmental period. (author abstract)