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 is 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 This again survives in public schools, but has been replaced by head teacher in other British schools (although headmaster is still often used colloquially, particularly in grammar schools) and is equivalent to the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. The term headmaster also survives in some American and Commonwealth private 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 housemaster (the master in charge of a boarding house). Some public schools use other titles as well.
The female equivalent is schoolmistress, which can be used with all the same prefixes.