HAHAHAHAHAA.
I love it when a kid thinks they are slick and try to secretly grow in their parents house or in a dorm. Do yourself a favor, grow up a little, get your own place, and then well finish this conversation.
Do you have any idea how large a plant has to be to produce any worth while bud? Do you know how long that takes? I think we know the answer to that. Wait till they drop and get fuzzy before you attempt to do grown up stuff.
seriously, give him a fucking break! can't you remember what it was like to be that age? he didn't ask for your moral, high and mighty opinion on the matter, or to be patronised. yeah, fair enough, not encouraging him to do it, but just chill out man.
besides, we all know that he, like most others, will probably do it anyway so you're just wasting your time. if you don't even have an answer for the question, why even bother?
to prosmoke:
if you had a filing cabinet for your school/sixth form work, your parents are unlikely to go in there and a filing cabinet is a good size for a stealth growbox.
an old, disused fridge? although not something that they're likely to suddenly want to throw out lol.
i made mine by taking out the drawers of my chest of drawers under my desk, fixing the fronts to a piece of wood and one set of the rolling things, so the door just rolls on and off in the same motion as drawers to.
good luck!