There seems to be a school of thought that suggests that the name of Brendon School was not named in the series until Turlough mentions it during
Planet of Fire. This was propagated on the DVD release of the story, and then re-affirmed in the new issue of
Doctor Who Magazine (#327).
Quite why this has gathered weight is beyond me; even though the school name isn't mentioned by a character during
Mawdryn Undead, it
is shown on screen, as you can see here!
It might not have been so obvious on the old VHS release, but the nice shiny DVD reveals all (grin).