I highly second Colinsmum's approach. We've taken this approach with DS's teachers in K and 1st grade, scheduling meetings early in the year with both of them, and it has worked well.
Gifted programs are set up for MG kids in the 98th/99th percentile, not HG/PG kids in 99.9th percentile; there aren't enough of the latter to fill a program. While good programs of any kind would ideally differentiate to accommodate a wide range of kids, I find that in most cases, we the parents have to advocate. Our school has been happy to accommodate DS, but only with us advocating for it and bringing his teachers onto our advocacy team. Hopefully you can bring your teacher onto your team by sitting down with her and sharing what he's currently doing and working with her on a plan to keep him challenged.
