Research Findings: The present study used a longitudinal design to identify how sleep habits and learning-related behaviors impact the development of cognitive skills in preschoolers (ages 3-5). Sixty- seven children with parental report and cognitive skill assessment data were included. Scores on the Differential Ability Scales (C. Elliott, 1990) were obtained at ages 3, 4, and 5. A Sleep Questionnaire (D. Gozal, 1998) with 12 items from the Child Behavior Checklist (T. M. Achenbach & L. A. Rescorla, 2000) related to children's attention and activity levels was administered at age 3. Growth curve changes in cognitive scores were estimated using hierarchical linear modeling. Parental reports of nighttime sleep duration predicted level of cognitive skills at 3 years. The effect of sleep duration on cognitive scores was constant across age. Practice or Policy: Sleep and learning-related behaviors distinguish the cognitive skills children bring to preschool programs and impact gains made in skills while in preschool. (Contains 5 figures and 5 tables.)