This is mainly due to the need to have a school year starting at the end of August and the requirement for a certain number of student-contact days before testing periods (particularly for the high school) that do not match up with all of the other calendared Japanese holidays. For some holidays, like the holidays in September, we deliberately schedule informational open house days on holidays to make it easier for parents who work to come to school. We do realize, however, that many families only have the Japanese national holidays as days together, so we try our best to strike a balance between those needs and the needs of our curriculum.