It is important to ascertain the accuracy of children’s and adolescents’ self-reported sleep estimates as they are usually the first (and sometimes only) measure of sleep taken by parents, clinicians, or researchers. In this study, sleep diaries were compared with actigraphy monitoring to investigate the correspondence between measures of sleep in children and adolescents and provide normative data. Differences in age, gender, and school day/weekend were investigated. Sixty-six (21 boys, 45 girls) children and adolescents (11–17 years) wore a wrist actigraphy monitor and completed a 7-day sleep diary. Measures of sleep onset, wake time, wake after sleep onset, and total sleep time were obtained. Less than recommended (9–11 h) amounts of sleep were obtained throughout the week and all participants underestimated the duration of their night wake. Children went to sleep significantly earlier and obtained more sleep than adolescents. Sleep onset and wake time were significantly later on weekends than school days for both age groups. No significant gender differences were found for any objectively measured sleep parameter. Correlations between diary and actigraphy were moderate to high and significant for sleep onset, wake time, and total sleep time. Paired samples t-tests indicated a significant difference between diary and actigraphy scores for all variables except children’s sleep onset. Overall, children and adolescents overestimated their total sleep time by approximately an hour, primarily through an under appreciation of night awakenings.