To establish the psychometric properties of a self-report measure of daytime sleepiness for school-aged children. METHODS: Three hundred eighty-eight children aged 8-12years (inclusive) from paediatrician s offices, sleep clinic/labs, children s hospitals, schools, and the general population were recruited. A multi-method approach was used to validate the Children s Report of Sleep Patterns - Sleepiness Scale (CRSP-S), including self-report measures (questions about typical sleep), parent-report measures (Children s Sleep Habits Questionnaire [CSHQ], proxy version of CRSP-S, Children s Sleep Hygiene Scale [CSHS], morningness-eveningness) and objective measures (actigraphy and polysomnography [PSG]). RESULTS: The CRSP-S was shown to be internally consistent (Cronbach s alpha=0.77) and the scale s unidimensionality was supported by a one-factor confirmatory factor analysis. A Rasch-Masters Partial Credit model demonstrated that items cover a broad range of sleepiness experiences with minimal redundancy, gaps in coverage, or bias against age, gender, or clinical groups. Test-retest reliability was 0.82. Construct and convergent validity were demonstrated with actigraphy, parental reports of children s sleepiness, sleep disturbances, sleep hygiene, circadian preference, and comparison of groups of children (e.g., sleep clinic/lab vs. school children). CONCLUSIONS: The CRSP-S is a reliable and valid self-report measure of sleepiness for school-aged children. As an adjunct to parental report measures and objective measures of sleep, the CRSP-S provides a brief and psychometrically robust measure of children s sleepiness. Children who endorse sleepiness should have a more detailed screening for underlying sleep disruptors or causes of insufficient sleep.