Teacher

A teacher was an individual who was well versed in a subject and made money by teaching others, typically children or young adults. The Doctor has encountered numerous teachers in his travels. Two of the First Doctor's first companions were teachers. Ian Chesterton and Barbara Wright, who taught Susan, followed Susan to a junk yard when worried for her safety and quickly became caught up in the Doctor's travels. (TV: An Unearthly Child)

The Second Doctor, Jamie, and Zoe, when visiting Dulkis, met Balan, a teacher and researcher of the residual radioactivity from a blast that happened 172 year prior. (TV: The Dominators)

The Third Doctor befriended Bernard Helmann, a philosophy teacher at Oxford, at the 1960 Campaign for Nuclear Disarmament. (PROSE: Come Friendly Bombs...)

The Seventh Doctor and Ace met Miríl, a teacher on Kirith, and uncovered the truth about the planet's history with him. (PROSE: Timewyrm: Apocalypse)

The Tenth Doctor posed as and met many teachers while investigating Deffry Vale High School with Rose, Mickey, and Sarah Jane. (TV: School Reunion)

The Tenth Doctor became the human teacher John Smith at the Farringham School for Boys for a short time when traveling with Martha. (TV: Human Nature/Family of Blood)

Clara Oswald, companion of the Eleventh Doctor, became a teacher at Coal Hill School after the events on Trenzalore. (TV: Day of the Doctor) At the school she befriended Danny Pink, another teacher. (TV: Deep Breath)