Coal Hill Secondary School first appeared in the first episode of Doctor Who ("An Unearthly Child" (Season 1)) filmed and set in 1963 which one of the students (Susan) is described as unearthly by a science teacher (Ian Chesterton) and history teacher (Barbara Wright). By the end of the episode all 3 are travelling with the Doctor and become his first companions. In the episode Susan stared:
Look, I love your school. I loved England in the twentieth century. The last five months have been the happiest of my life.
In "Remembrance of the Daleks," (Season 25) (an episode first shown in 1988, but set soon after the Doctor left in 1963) the Seventh Doctor returns to the school with the original series's final companion, Ace, to reclaim the Hand of Omega and fight Daleks. He was asked if he was applying for the caretaker position.
In "The Day of the Doctor" an episode filmed another 25 years later (but partially set the full 50 years after the previous episodes) Clara is first shown working at this school and has been ever since. The Doctor returned to Coal Hill while Clara worked a number of times and later became the setting (as "Coal Hill Academy) for the spin-off "Class."