You could write down all the things you want to achieve in relation to school and studying on index cards (e.g.
I want to get a UAI of .... , I want to get a ranking of .... in this subject, I want to get into this course at uni which needs a score of ...) and whenever you feel bored/unmotivated, whip out your goal cards and read them! Make them pretty and colourful too!!
You could also try reading them before your study sessions, to re-enforce your goals and what you are aiming for.
It sounds very cheesy, but it works for me!
Try it out; it only takes like 10 mins of your time to do.