Self-regulation of behavior generally refers to controlled, cognitive monitoring of the actions and steps required to obtain a goal, or to bring about a desired response from the environment. Age-related changes in self-regulation as well as individual differences at a given age or developmental stage play fundamental roles in shaping children's experiences and the responses children elicit from caregivers and others. However individual differences in children's temperamental emotional reactivity and the ability to control this reactivity are also important for understanding developing self regulation. This Spanish-language Digest focuses on emotional reactivity and its relation to the development of cognitive functions that promote self-regulation in young children. The Digest examines how emotions may influence the development of the cognitive functions that contribute to successful self-regulation and thereby to school readiness. Implications for caregivers are then detailed, including the following: (1) high quality preschool education programs can best promote school readiness by helping to secure the social and emotional foundation upon which children can build cognitive skills; and (2) preschool activities that exercise impulse control, sustained attention, and working memory are likely to promote the development of cognitive skills important for knowledge acquisition in the early elementary grades. (Contains 13 references.) (HTH)