Find out what's possible first. There may be restrictions on what a teacher or principal is allowed to do. In our last district the rules were different for math and LA. In principal, accommodating advanced reading in the classroom is much easier than advanced math, but it depends on the teacher. It's not uncommon to start K reading chapter books, you could approach it very simply - say you're asking if he can be in a class with the other kids who are already reading.
That's your aim and it also establishes that you don't think you have a little genius special snowflake, just a kid in the range of normal who needs a cluster.
