prefect; praepostor
A student leader in a boarding school or similar institution, responsible for discipline and supervision of other students. The term is primarily used in British-style school contexts.
He was chosen as a prefect and took on the responsibility of enforcing the dormitory rules.
The prefect checks the students' attendance every morning.
風紀委員 is a member of a school discipline committee, similar to a prefect but typically part of a larger group and not necessarily a boarding school role.
Compound of 監督 (supervision, direction) and 生 (student). The term is a direct translation of the English 'prefect' or Latin 'praepostor', used in Japanese schools modeled after British boarding schools.