Tell him congratulations - that's a lot of hard work.
My oldest was a straight A student and got picked on quite a bit. We put him in Tae kwon do and he excelled in it. It's not just about fighting. It gives them confidence. And teaches them that they don't need to fight - that they can walk away. But the skill is there when they need it. He has not been in a "real" fight since then. There was one kid in high school that wanted to fight him and another kid stepped in. He asked the kid if he thought he could win a fight with him and this kid said "no". Well, this guy here can mop the floor with me, do you still want to take him on? For some reason, people don't expect a straight A student to know how to defend themselves.
The majority of kids who take proper martial arts lessons do not turn into bullies.