After considering all the recollections, the answer seems to be:
sometimes.
There certainly appear to have been teachers using large adult plimsolls.
Others used ordinary children’s gym shoes.
Some selected shoes from lost property.
Some borrowed them from pupils.
Some kept the same favourite slipper for years.
And some apparently used whatever happened to be within reach.
The famous size 11 or 12 slipper therefore cannot simply be dismissed as a myth.
But neither should every childhood recollection of an enormous shoe be taken literally.
Memory, fear and playground storytelling almost certainly enlarged a few along the way.
