That is great advice, seaturtle, and what a wonderful teacher your son has now! Sometimes young teachers are just the ones who are pouring all their time and passion into serving their students. There are great ones out there!
I agree that asking about assessments, standards, and how to challenge the child and aim for a year's growth are all good ways of phrasing it, whereas "bored" is touchy. Teachers get defensive, because they get that from EVERYONE and it is often kind of personal. Of course a gifted kid might have an excellent, engaging teacher but if the curriculum is still too low, it's natural for him to be bored.