My senior college allowed us to smoke. I really don't recall anyone deciding that they were going to start because they could. I think by that time most of the kids who were going to smoke were smoking.
What I do remember is lots of amazing teachers who managed to make children who were on the verge of walking away from the education system re-engage with learning.

Personally I would prefer that children not lose their educational opportunities as well as their health if they are smoking. As for whoever asked about shooting galleries.... at the risk of a public lynching...... yes, if there were junkies at my children's school (which isn't likely since junkies tend to drop-out), then I would prefer that they were given a quiet corner in sickbay with a curtain and a sharps disposal bin and an ask no questions tell no lies policy, instead of using the toilet or oval and maybe leaving a needle where another child could get a needle stick injury.
There's no need to provide them with anywhere to shag - teenagers are expert at finding those places themselves