I'll see your anecdote and raise you another.

I can't do advanced math even the next day.

I went back to school when I was 30, for mechanical engineering and quit smoking because I needed to do well to get a job when I was done.

I was there to learn not just to pass so I pretty much got 100s on every math, engineering and physics class I took.
Except for Physics II my second semester.

I did all the homework so I didn't really study all that much, I already knew it.

So the night before the second of 4 tests, including the final, I smoked a joint a friend had given me a week or two before.

I got a 34 on that test.
I just couldn't figure out which equations to use.
I would spend like 10 minutes on a question, going through an equation tree to find the number I wanted and when I was done, I would realize that I had no idea what number I had just found but it surely wasn't the one I needed.

I got a B+ for the year on that class even though I got at least 100 on every other test (100+ if there was extra credit).
Hell, I got a 107 on the final and still got a B.

Anecdotally:

I have heard that if you study stoned you should take the test stoned. If you studied straight you should take the test straight.

And this was said by the test giver.

Every one is different.

and of course in the title Some People.

According to several psychology studies, your situation while learning information should be matched by your situation while retrieving it. That is to say, if you study drunk, you'd better write the exam drunk. So if you're writing a paper that's cool, because you are usually not tested on it after you write it. But don't study stoned unless you think you can write the test stoned.

http://forum.grasscity.com/real-life-stories/141217-doing-homework-stoned-2.html

I took the test sober, I got high the night before.

In my earlier iterations as a social sciences type I took the classes stoned and the tests stoned. I was lucky to get Bs. The only As I got were when I either kissed the teachers' asses or, in once case, got high with the prof as we both "dated" some cute students.

He was funny, he absolutely believed in Kesey's Combine.

Carl Sagan claimed that marijuana had its most beneficial influence on his ideas about social and political issues.

IOW, the stoned Sagan was responsible for "Nuclear Winter" and the unstoned Sagan was responsible for discussing real science.

I just remembered we've had this discussion before.