I don't think we really do anything different or unusual, actually. It's hard for them to refuse our requests when the results of various test scores (regular classroom, GATE, CMTs, IOWA, Otis-Lennon, etc. and so on) are staring them in the face. They can't deny that our sons need the enrichment. I don't know how they would react if the test results didn't support our requests.
I do have one rather cynical observation, though. When my youngest son was in first grade and was being evaluated for a grade skip to second grade, we met with the district curriculum coordinator to discuss the plan for his progression through the math classes. (He was skipped up the one grade, but he was also accelerated another full grade in math, which has made the scheduling a bit tricky.)
Anyway, we happened to mention that we had recently moved to town from out of state. She said, "We always love it when families with kids like yours decide to move here--it benefits the town and the school system to have students that score so highly on tests." Which I took to mean, "Your sons' scores on the standardized tests help raise the average for the town and makes us look good."
So since then, we've been very aware of the power that brings. When my oldest son was in fifth grade and was bored out of his mind because the teacher was in her last year before retirement and was almost literally sleep-walking through the curriculum, I approached the principal and asked for something to be done in addition to the regular GATE program that our son was in. He balked, because it was his first year as an administrator and he didn't want to rock the boat with the teacher. I casually mentioned that it would be a shame if we had to pull our boys out of the school and put them in private school--especially when the CMTs were coming up in a few months.
Within a week my son was being pulled out of the class for enhanced work in reading and math groups. And we had no problems for the rest of the year.
Is that bad, to use our kids' test scores as a bargaining chip?