Background: Sleep problems are a common complaint of parents of preschool children. Children with neurodevelopmental disorders have even more disrupted sleep than typically developing children. Although disrupted nighttime sleep has been reported to affect daytime behavior, the pathway from sleep disruption to sleep problems, to impairments in daytime performance or behavior is not clear. This multi-method, preliminary study assessed this path in 68 children with autism, matched to 57 children with developmental delay without autism and 69 children developing typically. Methods: Actigraphy, structured questionnaires, laboratory assessments, and parent reports were obtained in 194 children. Results: Controlling for diagnosis and developmental age of the child, nighttime sleep problems determined by parent reports were significantly associated with decrements in daytime behavior, also measured by parent report instruments. However, actigraph-defined sleep problems and objective measures of daytime sleepiness were not associated with decrements in daytime performance. Conclusions: Parent report measures substantiate relationships between disrupted sleep patterns and waking behavior. Further understanding of the pathway from sleep disorders to daytime sleepiness and decrements in waking performance, however, may require more rigorous methods of assessment such as polysomnography and the multiple sleep latency test.