As an imitator of a public school, Stogs used the term “master” for teacher.

Wikipedia says:

“A schoolmaster, or simply master, once referred to a male school teacher. This usage survives in British public schools but is generally obsolete elsewhere.

The teacher in charge of a school was the headmaster. This again survives in public schools, but has been replaced by head teacher in other British schools (although headmaster is still often used colloquially, particularly in grammar schools) and is equivalent to the principal in American schools.

A range of other terms was derived from this, including deputy headmaster (the second most senior teacher), senior master (used in some public schools instead of deputy headmaster), second master (the third most senior teacher), and housemasters.” (The pupils were divided into groups called “houses,” which competed against each other in sports and other activities. One of our houses was called Harvard. The others were Cure, Leek and Bingham).

I’m not sure of the origin of the term “master” but it certainly conveyed the idea they wanted to get across – that they were our superiors and we were there to submit and obey.