In response to the original question, here's a semi-relevant anecdote...
I called my twins' (public) middle school a few weeks ago to inquire how to opt my kids out of an administration of the Explore Test to all 8th graders (since they had taken the test thru Numats in 4th grade and were already pushing the ceiling then). This was the first time we had opted out of testing at this school, but when I spoke to the school administrator, he indicated that they have a few families opting out for every standardized test administration, and he specifically said this was the case for the annual state tests. I imagine the same would be true at most public schools.
