He's at a detention center for possession of marijuana?
I'd like to echo MedMech's statement of zero tolerance these days.
Anyone else remember being a teenager? Remember when authority pushed you, you pushed back? The harder authority came back, the harder you gave back? Remember how there was little logic and lots of emotions? Or was it just me?
For f@ck's sakes, the US needs to get its head out of its a$$ and realize that pot is as common as a glass of whiskey! Here in Canada you can light up a spliff in front of a cop and the worst he might do is tell you to put it out, as long as you're not being an idiot about it. As someone who has seen a lot of drugs being used and abused (I've been in a professional rock band for over 10 years) I can tell you I've seen a lot worse come out of alcohol abuse than marijuana abuse. In Vancouver you can buy pot anywhere you want, it's literally easier to get than alcohol - the dealers don't card you.
I'm not preaching on one vs. the other, all I am saying is that this all seems a bit extreme over a teenager smoking some pot. If the rest of his life is in order than your son sounds like 99% of the teenagers I have known and currently know. If he is abusing it and studies are slipping, he steals constantly, etc. then yes, I'd say he needs help as there are other issues besides smoking pot.
Funny thing is that most of the strictest (and sometimes naive) parents are the ones who usually don't see this coming - either because they were straight as rulers as kids or they simply forgot what being a teenager is like - a ballfull of emotions, angst and trying to fit in.
Just my $0.02 CDN...
P.S. I am happily married with a son of my own.