Objective: This study aimed to examine the sleep patterns, sleep habits, and sleep problems in Japanese elementary school children from the aspect of their developmental age. Methods: The Japanese version of the Children's Sleep Habits Questionnaire (CSHQ-J) was distributed to the parents of 330 students of which 296 (154 boys and 142 girls) questionnaires were returned. The subjects were divided into 3 groups by grade (Low-grade [1st−2nd graders], Middle-grade [3rd−4th graders], and High-grade [5th−6th graders]). Results: Bedtime was significantly later and sleep duration was significantly shorter in the older students. The total CSHQ-J score was significantly higher in the Low-grade group compared with that in the High-grade group. Regarding the sub-items of the CSHQ-J, the scores for "bedtime resistance" and "sleep anxiety" were significantly higher in the Low-grade group compared with those in the High-grade group. Conclusions: That sleep duration was significantly shorter in the older students was attributable to their later bedtimes. Differences in the total and sub-item scores of the CSHQ-J were largely attributable to the autonomy of sleep
