When I was a kid I read that mint flavorings can help the blood vessels in your head dilate, increasing the amount of blood flow to your brain and therefore helping you do better on studying and tests.
Whenever I have a test to study for or to take, I made it a point to keep some sort of mint flavored candy around, and consistently across the board I have always done better on tests than my peers.
That being said, it is entirely plausible that this is a placebo effect, but I like my placebo and it works for me. Perhaps it will work for you as well.