If you don't get any information, then you can contact school authorities (counsellors/ teachers) to get exact dates. Most of Japan's Public or Private's elementary and middle schools are closed on national holidays, Saturdays, and Sundays.
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Public elementary and middle schools are closed on national holidays, Saturdays, and Sundays. Japanese schools have three semesters, separated by vacations.
Saturdays and Sundays are generally days off and there are also many public holidays, but some workers in service industries and real estate have their days off during the week and spend the weekend working.