Here's a view from the other side. I was that aggressive, smoking dope in school time teen.
I had a lot of issues with bullying, smoking dope stopped all that. I didn't want to stop because it would have dropped me out if the 'in' crowd, which would have meant getting bullied again.
Peer pressure in a school with a lax regime against drug taking is IMMENSE. More so in schools with a zero tolerance policy.
I once found it hilarious to take a pot plant (LITERALLY a POT plant) into school and sit it on my desk and fall about in hysterics when my sweet, innocent, God fearing Geography teacher would compliment me on my lovely pot plant...
I only sorted myself out and stopped being such a knob when I fell pregnant with my DD just before I turned 16. I stopped smoking dope whilst pregnant and breast feeding (mostly because I stopped smoking full stop while pg).
But I took up smoking dope again by the time she was 7mo. (I stopped bf at 6mo).
It wasn't until I was 21, and had 3 DC's, that I stopped smoking dope totally, and grew the hell up.
(Note, I only smoked it when my DC's were in bed, outside, not around them, not a complete twat).
I haven't had any weed for 10 years now, and I'm 31. But I had to want to stop.
People DO come out the other side in the end, most of the time. All the dope fiends I hung around with are now married with multiple DC's, very respectable, some on PTA's etc.
I would 1) Do regular room searches, and bin any drug paraphernalia. 2) Have a talk with him about his future. 3) Go for tough love and explain that he can only live with you if he is either in education of some sort, or work.
Good luck.