I don't think they're going to get lost. The schools are usually designed very simply and plainly, just straight multi-story buildings with each grade occupying a floor, like 1-1, 1-2, 1-3 all being in a row, so it's not likely anyone would get lost per se. It's just a bit of a taboo to cut through other grade's floor just for a shortcut where they might get stopped by annoyed senpai.