“It may come as a surprise American exchange students, but in Japan, students clean their own classrooms as a matter of course.”
A matter of course is something that is routine and unremarkable, to be expected.
「アメリカの留学生は驚くかもしれませんが、日本では生徒が当たり前のように自分の教室を掃除します。」
「A matter of course」は普通な、日常的なこと、当たり前なことです。
