What Angel is saying is definitely the right and responsible thing to do, but sometimes this can backfire, I've seen this before personally in school myself where a boy was being bullied and he told the teachers and his parents came to school to talk to the other kids parent, the boy who was bullying him was only suspended for about a week, once he came back he was so ****ed that the boy had told his parents that he beat the crap out of the boy the moment he saw him. Afterwards the boy who bullied him was put into another school away from him but his friends still continued to hold hostility towards the boy for getting their friend sent away from school.
I'm not trying to discourage you or anything only telling you how it is from my experience, its definitely the right thing to do to tell adults, but this is no for sure way to end the bullying completely since while it may work sometimes and the boys parents are able to change their kid for the better, it also can make it worse if the boy does not learn from it and instead only starts to hate you more.