D.F.
Someone at school has to be informed - I might start with the school counselor, who might be able to help your son problem-solve this in confidence and who can hear your concerns about possible retaliation against your son for telling. Of course your son wants this so remain a secret - it's embarrassing for anyone to admit they are being bullied! If it were me and you for some reason judged that it was not safe to approach the school with this (e.g., is this kid or his friends gang involved? Capable of physcially hurting him?), I'd consider moving him elsewhere and then enrolling him in some sort of martial arts training program so that he could 1) gain some confidence, and 2) defend himself and learn how to handle being bullied.