I used to smoke weed everyday and my grades sucked then i cut down because i didn't feel as high anymore so i did it once every weekend and my grades still sucked then when i got put on probation my grades got better not because of the weed it's the motivation if i get shit grades my probation gets fucked over witch isn't fair but can't really do anything about it I don't think weed really has any effect on your grades unless your high doing your school work I think it's more of a motivation thing...well atleast for me that is