Hi--
I just went through this with my daughter's school, with great results. I feel so lucky! I think what may have helped was that her current teacher is the one who initially approached the principal. Their immediate response (to full-grade acceleration in the fall--skipping 3rd grade) was no no no, we NEVER do that, etc..., with a note that they would "be glad to meet with us should we like to discuss her placement.."
So, we set up the meeting, got the Iowa Acceleration Scale, copies of all her test scores, asked the 3rd grade teacher who is currently teaching DD reading to join in the meeting and went in preparing for a battle. The meeting went really well, with the asst. principal playing "devil's advocate" (her words) with regard to social issues, but mostly everyone just actually listened to us. They were actually kind of immediately influenced by her test scores (IQ, achievement, and above-level) and suggested right at that meeting to move her to 3rd in math as well as reading.
They agreed to read through the Iowa Scale and set up another meeting 3 weeks later. Two days after the first meeting, the principal called and told me that she would like to use the Iowa scale, would be observing dd in the classroom (both 2nd and 3rd) and said that she though dd was a good candidate for acceleration.
Well, we just had the second meeting and they agreed to the full-grade acceleration, and actually moved her up full-time for the remainder of this school year as a transition. The principal told me that initially she was deadset against it, but that she was impressed by the amount of research and information we provided. She said it is obvious that the acceleration is "what needs to be done."
I did not fill out the Iowa Acceleration form ahead of time (I did it on a separate sheet at home for my own information), and kind of let them think they were in charge. I was actually prepared to go with subject acceleration, but we thought for the sake of the meeting, we should stick with requesting full-grade, so that even if they didn't give it to us, we could back down to the subject acceleration.
So, I would say to try to let them think they know best, but don't back down. We did a lot of, "yes, we have thought of that and are concerned too, but...." If the first meeting doesn't go well, you can always get more demanding, but I think it was best to keep it friendly. I kind of approached them like, well, you as experts in education can see that she needs more...
Anyway, I know we were very lucky and it's not always that easy, but I am just relaying our experience.
Good luck!
