You're right to be sensitive that others will react to this news with their own biases. For some reason, I think if you ever say your child is gifted, what people hear is you calling their child dumb, or at the very least, "less than."
I agree with the first couple of posters who suggested you should say it's a better fit for your son. Or you could also add something like, "after talking it over with the principal and his teachers, we felt like he might do better at a different school." If they ask why, "Oh, lots of reasons. Is that bean dip?"
We never discuss my son's placement in a school for highly gifted with people outside our family, except to say that he really enjoys it and we love his teachers.
