Send her a small box of good chocolates; a thank you card, thanking her for the things she does well; and maybe some books for her classroom(if she has a classroom selection of books). Keep on helping, as you've done, and give the school time to test and give the teacher a bit of time to process what you told her about your son's abilities. Just be sure the school doesn't drop the ball on testing, and be ready to bring up the subject of math acceleration when you see a good opportunity.