This sounds just like the original school I had my dd9 in from K to grade 2. She was getting very depressed. We ended up moving her for third grade and it was the best thing we could have ever done for her. At her original school, their idea of G/T for 45 minutes pull out once/week and extra worksheets. Like your child, my daughter makes some mistakes along the way, sometimes forgets to answer questions, etc. She has a GAI of 143, some WM issues, but a high processing speed...so, she works very, very quickly, thinks quickly, but will make little mistakes along the way. This has gotten MUCH better over the last two years. I was worried about ADHD for a while, and though she has what I call adhd tendencies, it really seems to be more a matter of her brain being consumed with the bigger stuff over the small details, as Dude states. Anyway, to look at kids like ours and focus on their mistakes instead of their gifts does them a huge disservice. I think many educators forget that our kids really can be quite asynchronous in their development.
We have had to really work at getting dd to go back and check her work for those little mistakes. She doesn't really like to be bothered to do it and considers it to be a waste of time and boring. Anyway, I feel your pain and we were in your exact position not long ago. If they are not willing to work with you at the current school, is it possible to put your DD into another school situation? Where we have our DD9 now is not perfect, but it is so much better than where she was before.