I'm not sure there's much value to having a specific number. As the borrowed quote said, "Lots of our high ability kids go in eager to be finally going to that place where everyone learns." That's a personality trait that can't be measured on an IQ test.
Really, the questions are:
1) Is my child learning anything valuable in school?
2) If not, how is she responding to that?
Because sometimes they are learning something valuable, even if it's not necessarily reading and math.
My DD, who is MG, went to pre-K, where her teacher told my wife flat-out that she had nothing to teach our DD. That wasn't precisely true, but it is illustrative. Anyway, this teacher was very fond of DD, embraced her abilities, and gave her the chance to shine by letting her do things like taking over story time, reading aloud to the class. This was a very positive experience for DD. She was well-liked in class, emerging as a leader, and generally building a wonderful self-concept. So the answer to question one was an emphatic "YES," even though the teacher said otherwise.
Then came K, in a different school district, and the answers were "no" and "badly." We didn't need a higher number to tell us that something had to change.
