[justanotherc]

Well not if you ask him as he would tell you his grades were highly correlated to his smoking habits. Obviously its a non scientific anecdote, but my point is I thought it was well established common knowledge that marijuana affects cognition.

[appletrotter]

And his smoking habits might be directly correlated with reduced motivation, poorer time management, and any number of other things. Meaning that it might not be a direct cognitive effect, but a second or third order effect altering his performance.

[justanotherc]

Please read the second part of my comment before just repeating what you already said