I'm late to this discussion, but am prepping for a similar meeting next fall, so I'll add a couple of thoughts.
First, this site has some very good resources. For short-term review, I would suggest reading Julia Osborn's article on advocacy (you can find it easily using the site's search function). The article library also offers a Davidson Advocacy guide, which, though it's 40 pages long, reads quickly and has good outline ideas. If acceleration is your goal, there are any number of good articles in the 'Davidson Database' article library. I read about one parent who brought in several such articles, with key points highlighted, and presented them in a binder to the school representative.
Second, a portfolio of your child's work/play in math, reading, whatever, showing a level of competence above what the school curriculum offers at the age-appropriate grade level, is hard to debate against.
Knowing your blind spots is key, too, if you can manage it. Mine is that I'm apt to rely on personal intensity rather than dispassionate data - this always backfires! But it's a terrific effort to be detached where my child is concerned.
Best of luck.
