I don't think there really is much of a link between the two. Lazy people are lazy without the help of marijuana, same with stupid people. I don't think it helps, but if I found out my kid did it I'd sit him down and talk to him. Tell him I didn't think it was a big deal but if I saw him getting into serious drugs (anything addictive; coke, meth, heroin) I'd intervene. I'd also intervene if I saw his marks dropping, because even though I said I don't think there is much of a link, it also wouldn't be helping.

My parents know I smoke pot but they are ok with it. They are ok with it because I have other hobbies (music, musical theater) and it doesn't seem to be affecting my grades. Right now I have the highest marks of the class in every class I take and I smoke pot every night (more than I ever have before).

If you want to show some parenting, treat your kid with respect when you talk to them and don't lie to them. I think that is the best way.