In the U.S. principle refers to the person who runs a school, whether elementary, middle or high.

In other countries, principal can be the head of a college too.
In some areas principal is not used for heads of middle or elementary/primary schools, which are headed by a headmaster.
Some schools have houses, house masters and prefects.
Schools, usually "public" schools have several houses where students live and eat their meals. The division among various houses is not based on class/grade/form/standard. A house includes students of all forms/grades. Pupils (another word I have not heard used in the U.S., where student is preferred), are fiercely loyal to their houses. Houses may have a "house song". One of the teachers lives in the house and is called house master. Schools that are not entirely boarding schools or are not boarding schools at all, may also have houses. Prefect is a student leader, who may wield considerable power and are responsible for disciplining other pupils. They may administer punishments too, on rare occasions, even corporal punishment.
When you are a university/college student majoring in economics, you are reading for an Economics Hons a degree. You sit for exams instead of taking exams and are awarded their degree/diploma in a convocation/commencement/graduation.

In some countries a diploma is inferior to a degree. A degree course/programme is more intense and may take longer than a diploma course.