Forgetting the above posts and I will say what my motivation is.
My motivation is myself. I am the one who wants to improve, I am the one who wishes to get result and I am the one who will get the consequences for my poor (or hard work).
I am usually proud of myself for working hard in most of my subjects but I sometimes let myself down.
By the way, another motivation for me is my mark (wheter it is good or not). If it is good, I am happy so I want to do better. If I get bad mark, I want to get out of that bad-mark-cycle. Either way, I know that I will improve.