...demand wouldn't change... ?? I believe demand would DECREASE since the incentive for pushers to lurk around elementary school playgrounds and give some product away to get new customers hooked would be gone.
If kids decide to try using drugs, it's usally because of their peers at a party, not because of some guy in a dark trenchcoat hanging around the schoolyard. When I was young, we always got stuff from older siblings or friends, not by driving into the inner city or talking to the local burnout.