I think your framing this the wrong way. There's no point trying to inform the teacher unless you want something to change. And the way you keep phrasing things I'm not sure. Do you want acceleration / differentiation etc in school? If so what you really want to do is to start and explore what options already exist in the school and find out how to take advantage of them. Any discussion of your son's ability should be in the context of why he needs additional challenge. If not (which is fine - its only K) then I don't think you need to feel guilty in any way about enriching at home either.
