Kindergarten readiness is characterized by important achievements in the acquisition of content knowledge and development of self-regulation skills—effortful control and executive function—needed for controlled and focused behaviors. Development of these readiness skills begins in the preschool period, and there is now strong evidence that these preschool skills are critically important for children’s academic performance in kindergarten and through elementary grades. Therefore, the focus of this chapter is on the preschool and early elementary periods (kindergarten through third grade) and the roles that sleep habits and sleep problems play in the development of cognitive skills, temperament, and executive functions. Research models, methods, measures and findings reported in published literature involving young children are reviewed and integrated into a framework identifying the influence of sleep on children’s skills and behaviors and suggesting that, at least for temperament, child characteristics may influence sleep.