Thank you to all for your responses! I've heard back from the teacher that this happens more often than not when they're doing math. My daughter is strong in both subjects, at least in comparison to her age peers, but she's more often paired with kids on her reading level when they're doing language arts work, so the impatience isn't as much of an issue.
I think the perfectionism thing is really on target--and related to meltdowns she's had about grades this year (the first year her school gives grades).
Definitely going to look into getting her involved in something that doesn't come so easy.
