This would not normally be used as a professional title in direct address, but there is a fine passage in Our Mutual Friend, by Charles Dickens, which demonstrates how it can be converted to that use. Bradley Headstone is talking to Eugene Wrayburn,...

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,...