1) So the girls aren't biological siblings, fwiw. Oldest dd12 has DYS scores, and a recent grade skip that I think at 1/2 way through the yr. I can call successful.
Just a side note, but I wonder how often that happens that two adopted kiddos are both HG+ (not distrusting your instinct at all, it is just curious re the nature/nurture/heritability stuff). Perhaps the birth moms chose your family b/c it was a "fit," though and the giftie aspect of things was part of that... musing over...
eta: I realized with your younger dd being adopted at 10 months of age that I was probably totally off on that musing in that there was likely no birth mom involvement at that point and that you also said that they weren't biologically related, which doesn't necessarily mean that your dd12 is adopted too. So, just ignore my above stream of thought there! Sorry.
2)I think there are prob. a lot of gifted kids, but prob. a lot of bright high achievers with tiger parents who I can see prepping their kids for tests. This particular school cluster seems to be known for insanely competitive crazy parents who all think their kids are gifted--I have not actually met any of these people yet, but I suppose they must be out there. I don't think once/week pull-outs are that great, and I think even a skip prob. wouldn't totally be a solution, but I guess it would put her closer to middle school and more options. I think the school basically thinks there is such a large number of gifted kids that the regular classroom should meet their needs without much effort at differentiation. I have no idea if they would be receptive to subject acceleration or greater differentiation. The assistant principal does have a gifted certification and is very nice and handled the IAS process for dd12, so I think he would be a good ally.
Yeah, we have some of that here too with kids who are prepped a lot and retested until they get into GT. I'd also agree that once/week pull outs are totally insufficient and lack of differentiation within GT programming drives me nuts. Not all gifted kids are functioning at the same place and the needs are so diverse.
Subject acceleration is a good place to start, though, if the school is game. That was probably the best fit we had pre-skip for dd14 and it is working pretty well for dd12 in math right now. I'd rarely expect a skip, a GT pull out, or subject acceleration to actually fully meet the needs of a gifted kid, but at times it is better than the alternative.