Knute has some good advice.
WARNING: Rantings of a very jaded, cynical parent follow.
I may just be too cynical, but I'd also be prepared for them to dismiss whatever evidence you bring in. Our experience (and the experience of a lot of people we know at different schools) is that it's common for staff to look at what you brought in and just flat out not believe you. If you show a book, be prepared for them to say that she doesn't really understand it or to say that it's not uncommon for kids to read at that level in their K. (If they say this, I'd ask how many the K teacher saw reading at that level at the beginning of this current year and how she knew.) If you bring in math, no matter what the types of problems are, they might dismiss them as her having been taught how to compute but without really understanding the concepts.
I never did figure out how to counter this attitude, and we ended up leaving our school because of it. No matter what evidence was presented, the teachers and administration had an argument why it wasn't valid, or they would just refuse to look at it, saying it wasn't relevant because it's not their curriculum.
If you do have a difficult meeting, then that is valuable information to have found out. If the administration is not supportive, then it's better to know that now. Conversely, if the administration is receptive to what you bring in, then that's a great sign and also good to know.
