Good Luck Suzie,
Remember that it may be best to consider this meeting as a first step. I tend to find the WJIII grade equavalents a little murky. Be prepared that the school won't accept them at face value (and neither should you) - going to an online curriculum for a test drive, such as Aleks.com to see how your kiddo actually does on 6th grade math will tell you alot about what you need to ask for.
I think that if writing is working well, and she's moved the reading level up, then a skip might be better kept on the back burner as an option. I won't deny that sometimes a needed skip is best taken when there is a severe teacher problem that you want to get out of gracefully. A terrific teacher is such a gift. Average teachers are still a gift IF you can get your child into a classroom where the readiness of the child matches the readiness level of the other children in the room.
I think of it this way. The teacher is the one to talk to about issues within the classroom. The Principle is the one to talk to when the solution lies beyond the single classroom. Hopefully you will get the Princ on your side and be able to hand pick future teachers. This can make all the difference.
Most schools believe that their 3rd grade Math is equivalent to everyone else's 5th grade math. So be prepared to ask them how they would suggest evaluating where to first try him in math. They will likely say 'end of year tests' - at this point remember to negotiate that 80% means that the next highest end of year test should be given. Afterall, how many kids are promoted to the next year with 80% or less? You are allowed to ask this question. In fact, it's usually useful to ask the sort of question that allows the participants to discover the holes in their logic as they are answering you, especially compared to pointing out holes in their logic. Logic isn't universally revered. Metaphores go a lot farther. Folk tales...anything to create an emotion of 'do it my way and it'll all be ok."
My favorite book for practicing my negotiation skills is "getting to Yes' by Fisher and Ury.
Best wishes, take notes, remind yourself that everyone wants whats best for your child. Print out what you like from here and keep it where you can refer to it.
It's important to write a follow up email while it is all fresh in your mind about who agreed to what.. what the options are...what needs to be found out.
We'll be waiting here with a dry towel and cold compresses. And virtual beverages of your choosing.
Grinity
