The scene is certainly part of the canon (everything is) it was broadcast once and has been seen on the re-runs, VHS and DVDs ever since (the original broadcast can't be broadcast again because of music use rights).
The same is true of Silver Nemesis which includes the same claims.
The Doctor had to go to the Academy to become a Time Lord. Why he had such a low achievement record is anyones guess. Maybe he was a bit of a Shobogan in his youth... I know I was.