at least one problem i see here (besides being asked for an opinion and then only the first two pages were even considered ... ):
let's say i want to craft a disengagement ring. then i would need to make the silver bars needed for the silver ring outside of "school", because they wouldn't materialize when i made them inside, same goes for the polished ruby needed ...
my suggestion here would be, like proposed originally, to have the items not being able to leave the schoolarea. Besides opposing this idea . but i agree that Entropy's idea would probably be easiest to implement.