I'm an undergrad right now, previously was a philosophy major, now a biological sciences (pre-med), and I smoke fairly regularly. I'd like to think of myself as a highly intelligent individual, and naturally school comes fairly easy to me. I have a great memory, short-term is a little iffy sometimes because I smoke often (1-1.5g a day usually); but, I'm able to remember almost everything (I have a photographic memory). I can't you know, read the previous slide in a powerpoint if the professor hits the switch too soon, but I can remember exactly where everything is in my place, or anywhere I go, without thinking about it.
That being said, I've so far been able to manage a 3.08 in my first semester at college while I was a philosophy major (gen-ed classes - ENG 105, History, etc). I was in a Fraternity then, so I was drinking a lot with them and spending a lot of time away from my dorm. So I never spent any time studying, or reading material for class. And I managed to walk away with decent grades. Then in the spring, I started working out a lot, taking adderall here and there (10mg), but still smoking probably 3x a week. Good weed too. And I took a BIO 100 class because I really wanted to take a science class (I was unsure of whether I wanted to go into Law School with a philosophy degree). I got an A+ in that class, aced the first test, nearly aced the 2nd (missed 1). I walked away from that semester with a solid 3.93 gpa. And now I'm going into my 2nd year, taking a full load of science classes with a statistics class as well, and I'm on top of it. I need to work on my study habits now, getting used to studying high as a regular thing. I'm extremely into my classes, I do terrible in my lab if I'm stoned before. I can't do shit in it, its at night, and its pretty fun, you forget what time it is, but if I'm baked, I can't do it. It usually is pretty easy, and straightforward to me, I get it. Its working with bacteria learning how to work with staining and identifying them, and having to work quickly (staining in under 5 mins - including finding it on the microscope). Albeit, I have two friends in the lab and the lecture, so its easier studying with them stoned.
One thing though, that somewhat remains constant now, is I've started taking my adderall prescription again. I have pretty bad ADD, and adderall calms me the fuck down. It lets me focus, but most of all it makes me not want to be moving around so much. I'll take 10mg-20mg a day, usually 10mg IR in the morning (half a pill) when I wake up will last me all day until the night. I try to eat throughout the day, so its usually pretty smooth all day with a little extra kick. I don't drink caffeine, haven't really since last year. My tolerance is so low now that an energy drink has me sweating, its hot out here to begin with, just becomes extremely jittery and uncomfortable.
All in all, I've started to look at my decision making going out, and I've been reconsidering a lot of choices I make, and working to better them. Ie: studying, being on top of my classes much earlier than their due dates (though, I work better under pressure with classes). I guess in the end marijuana is a relaxing, soothing drug that helps me wind down my day. But when it comes time to focus on things, it depends on the weed, but I can usually get right into everything and be fine. Studying high is fine, I try to read everything I need to know once over the night before, then read it over skimming the next morning. I'll have great retention, not necessarily long-term; but, when I review the same information later on for another class its right there. And picking it up again is no problem at all. I know the adderall is probably the biggest factor here, but its a low dose, and it seems to work perfectly with smoking.