STUDY OBJECTIVES: To evaluate a novel sleep education program for low-income preschool children and their families. DESIGN: Randomized trial of an educational intervention. SETTING: Community-based. PARTICIPANTS: Head Start preschool families (n = 152) in greater Lansing and Detroit, Michigan. INTERVENTIONS: Classrooms or Head Start sites were randomized to an intervention group (prompt intervention) versus a control group (delayed intervention). Parents attended a one-time, 45-min sleep education program and preschoolers received 2 w (320 total min) of classroom sleep curriculum. MEASUREMENTS: Parent knowledge, attitudes, self-efficacy, and beliefs were assessed as the primary outcomes just before the 45-min sleep intervention, immediately postintervention, and approximately 1 mo postintervention. Parents reported their child's bedtimes and wake times on 7-day sleep diaries at baseline and at 1-mo follow-up. Average weeknight sleep durations and bedtimes served as secondary outcomes. RESULTS: Linear mixed models showed a time × treatment effect for parents' knowledge, attitudes, and self-efficacy (each P < 0.05) but not beliefs. These improvements were found immediately postintervention but were not retained at 1-mo follow-up. Children in the intervention group improved their weeknight sleep duration at 1-mo follow-up by 30 min (11.0 ± 0.9 h vs. 10.5 ± 1.0 hours at baseline) compared to controls (10.4 ± 0.9 h versus 10.5 ± 0.9 h at baseline) (P = 0.04 for difference between groups). Children did not show statistically significant improvements in bedtime. CONCLUSIONS: Educational interventions in early childhood can have an effect on parents' sleep knowledge, attitudes, and self-efficacy, and on children's sleep behavior. However, repeated exposure to the new information may be important for parents as well as their children.