I'm almost 20 and finishing my sophomore year of college. Back in February, I was expelled from the University's dorms. On the record, it says I was evicted for smoking weed but there were a lot of underlying circumstances beyond my control and rather then trying to get to the bottom it if they just kicked me out. In addition to having to spend about two grand of my job money on fines from the school and leasing a place to live (I'm not denying guilt here, only pointing out that I handled the incident myself) , the school called my mother (while she was on vacation) and told her I had been evicted. She was furious at me and can't get over the fact that I smoke weed. I imagine a phone call from your son's resident director is probably one of the worst ways to find out your he smokes pot.
Since the eviction I've found a much better place to live and my grades have improved a lot. I hit a bit of a low spot academically that happened to coincide with when I got evicted. My mom got so mad because she thought the weed was bringing my grades down. In reality, I was taking some really challenging classes at the time and have since changed my major. I had a 3.4 GPA for the quarter last summer while smoking daily, so I know that wasn't the reason my grades were slipping.
I just don't know why my mom is so opposed to weed. She's a staunch authoritarian and believes that all laws must be followed by the book, so that might have something to do with it. Both of her brothers drank heavily (one was kicked out of college altogether) and did a lot of hard drugs when they were my age. Also, her father was a raging alcoholic for most of his life and died of liver failure after having been kicked out of the navy for drinking on the job. I see where she's coming from but all the past problems on her side of the family were related to alcohol, not weed. I might have an occasional beer but other than that I don't drink. I hate everything about alcohol, how it tastes, how it burns, and especially how it makes me act.
I'll be heading home for a weekend soon, and I'm sure this is going to come up. How can I have a conversation without her blowing up? She won't listen to my point of view at all (I quit trying a while ago) and my Dad's too afraid to take sides (he told me he smoked back when he was my age but he's not going to stand in her way). I've always been a hard worker and graduated high school with a 3.6 GPA. I never question her about the way she does things and I'd never bring the habit home with me, but she can't seem to let it go.

