Hi again mom2two,
Well, your question is a good one. I'm not sure what your school offers, if anything, for a gifted program. Gifted programs are not mandated nationwide and numbers of them are dwindling due to lack of funds. As a result, you may not have an option of entering into one. If this is the case, you may want to research Montessori schools which are geared toward letting students work at their own place. I've toured a few and was VERY impressed.
In regards to your question about approaching the school with the scores, I don't see how it could hurt. Unfortunately, people who don't work for the school system have this idea that schools try to squirm out of their responsibilities to provide kids with the best education possible whenever they can. I have worked for a total of 11 schools during my career as a school psych and have never had an administrator take this approach. I can't see why bringing these achievement scores to their attention would be an issue. By the way, I noticed that no one answered your question about whether achivement scores can be higher than IQ. This is a definite possible and somewhat frequent occurrance. In this case, he would be regarded as an "overachiever" since he is workign above where his ability assessment predicts that he would. When you're talking this high of scores, however, it's really not as big of a difference as it seems. His IQ establishes that he is bright and that he will excel at many things and that is what he is doing in the acadmeic areas. The discrepancy between the two with scores in the high average range and higher is really an afterthought.
I want to stress, once again, that you shouldn't feel skittish about bringing the scores to the school. Any school worth their salt would already have some type of assessment to go off of anyway (Brigance, etc.) so I wouldn't think that it would be anything groundbreaking to them that he is bright. I'm just not sure that they will be able to accommodate him depending on what state you live in.
My other question for you is whether or not the person you are going to has provided you with valid scores in the achievement range. I admit, I have given a WISC when a WPPSI was called for because I did not notice the age, however, I quickly gave an alternate assessment when I discovered the error and threw the other score out. If your tester is adopting a "oh, huh, I wonder why I did that" attitude, I would be concerned about the validity of all scores. I must admit that a kindergartener with 5th grade skills is something I have not come across and is hard for me to fathom, especially if he is self-taught. If you don't mind me asking, what are the credentials of this individual?