I was initially bullied when I went to secondary school, but I had a guardian angel in the form of the much revered head boy who lived next door to me. Being a few years older he would leave well before me, exposing me to the bullies once more 
I found the answer was to single out one of the gang of bullies and get at him first, he was bigger and tougher than me but I went in with all I had and he was so stunned by my picking on him that he actually gave in and ran off with a bloody nose. Word got round of my so called fearlessness and no one ever bothered me again.
My Son is very mild mannered and was bullied when he lived in Wales with my ex wife, but he then moved back to live with me and attend a far bigger school. One night I saw a gang of bullies beating up one boy and waded in calling them a bunch of cowards, they were all around 18 years old, I took the side of the lone kid and told them that 10 to 1 was cowardess, so try 10 to 2, they went away, but word got round again and no one ever toughed my Son for fear of reprisals from me. 
Give as good as you get just once and the bullying stops 