Well he said he would install it though nLaunch, so no problem here.
Something that could be done but I don't think there are any programs for it (there are programs that do similar things though, like
RootDoc but this one does quite the contrary of what you want, it goes a step upwards instead of downwards) would be to create an empty Documents folder inside the Documents folder, then you set a program at startup that sets the empty Documents folder as the default folder, if you see what I mean. This way, you just have an empty calc until you remove that program from your calc (with the help of a computer) and reboot.
I also thought you could trigger exam mode, but I don't know if teachers will do a stupid wipe, like "delete all" or a full reset via the maintenance menu, so maybe that would be ineffective.