Jonette -
As a mom,(I'm not a professional), I wanted to pipe up that with scores like your son's and knowing that biological sibs are usually within 10 IQ points of each other, there is no doubt in my mind that you daughter COULD be underchallenged with only a single grade skip. Would the school be willing to use single subject acceleration in a few subjects to get a better fit? Try http://www.davidsongifted.org/db/Articles_id_10044.aspx for a review of a book that's a helpful reference.