Here's my findings concerning marijuana and school (and me):
High School - Marijuana = 2.9 GPA
College + Marijuana = 2.9 GPA

In conclusion, marijuana neither hindered nor helped my average. Going to class stoned, especially in subjects that were interesting, made me want to participate and ask questions more than I would in a sober state of mind. I wouldn't suggest marijuana when the class calls for mathematics or statistics or if the teacher is very monotone when they speak. As to a schedule I went by, I'd smoke a bowl or two before I headed out to class so I was pretty much baked when I arrived, peaking in the middle of lecture and coming down at the end of class.