Is it his principal?
If so, what is his relationship like with his principal? How about his relationship (if there is one) with his new teacher? Could/should he start with the teacher, or is that a bad move politically?
So much depends upon the teacher, the kid's reputation and the relationship (if any) between the two of them. Some kids could march into class on Day 1 of the new year and say to a teacher "Please! Challenge me!" and some kids would get strung up for something a lot more subtle than that. Obviously the ones in the latter situation had better start with the principal!
Can you tell us more about the advocacy situation your son faces?