During school, I didn't play a single game during the whole semester simply because I didn't feel the need to. OP, I think you should find out whatever activity you are avoiding by playing LoL. Very often, addictions are not because of what we use to satisfy our addiction but rather what we are avoiding by using our addiction.
I play loads of games out of school, but play very rarely while in it... It is simply because I don't avoid my schoolwork, I find schoolwork challenging and rather fun sometimes. I simply have no need to avoid it, what need do you have to avoid whatever else it is that you should be doing?