My kids are younger but this discussion is interesting to me because my kids are also tending to make those EF-type errors. DS is 8, but in 6th grade math and he recently did long division with lots of digits and decimals, and there were tons of careless errors. He knows all the steps and conceptually understands it, but seems to drift off in the middle of problems and isn't necessarily even copying the problems correctly (although this could be from dysgraphia). With one problem he got so fed up that he attempted to do the whole thing mentally, it was something like 766.22/ 33.88. Needless to say he got it wrong on his test. He thought it was acceptable, apparently, to just "estimate". DD on the other hand seems to have full-blown ADHD but she is meticulous with her math and rarely makes careless errors. She is excessively slow, though, and it could easily take her 5X longer to do the same problem as DS whipping right through it.
Unless DS improves a lot with his EF ability I'm anticipating problems down the line as the math gets harder. I'm not opposed to having him repeat any material that he's stuggling with, and see flexibility as the key with these accelerated students, although I don't know how that works once you are in high school and you have credits and grades on transcripts.
We are also seeing this for the first time with our 9-year-old, accelerated to 6th grade math. Huge grade drop got our attention. Seems to be a few things: setting up problems in a clear, consistent manner (the clear part is harder when your handwriting isn't too neat and the spaces are small), checking over the work, rechecking. He's made a lot of progress with those things.
For the original poster, I would think perhaps this is an important time to coach her through approaching a challenge and figuring out things to try to overcome it. Based partially on personal experience and partially on our son's experience of finally hitting a struggle. It's easy for girls and particularly, gifted girls, to hit that first set of bad grades and to decide they are no longer good at the subject.
