Think it depends on the subject aswell. Like for maths i find that if i concentrate when am taught it the first time, and understand it, it generally stays with me. And I don't have to do much revision, but for chem I js can't remember the colours, eurgh....
But there are naturally gifted people. My friends who's sound but is a bit of a chav and never turns up to his computing lessons, always running away from the teacher (quite funny), and nearly had a fight with another teacher. But in his ASs he came top in the class, beating loads of people who love their computers, lol.