The biggest obstacle to getting information into your memory banks and then back out again is anxiety, and you'd find it very difficult to feel anxious while you're relaxed in hypnosis!
We are generally taught as children to get all anxious about studying and writing exams. Lots of children are taught to dread handing their parent's their school report card every term. This anxiety is transferred to the body in the form of tension, and tension and anxiety does not help at all. This tension and anxiety is often carried through to adulthood.
Hypnosis has shown that the sub-conscious mind remembers everything. Everything that you have ever experienced is filed away in the sub-conscious mind. It's impossible to forget anything with the subconscious mind. For this reason you may have heard of the police using forensic hypnosis to help a witness remember a number plate or some other important detail while solving a crime.
Using hypnosis it's very easy to condition the mind to be relaxed and focussed while studying and to be relaxed and focussed while writing exams. Just the lack of tension makes a tremendous difference, but other techniques in hypnosis are easily used to further enhance memory and recall while in hypnosis.