That how I would approach it as well - like 'most likely there was an innocent mistake, a typo...' I'd bet money the school will say "oh my! yes of course there has been a mistake we will change them."

Howler's point that "It's not as though this is a transcript that colleges are going to look at" is true too, which is why I don't get hung up on grades (and the fact even when my son has mastered the curriculum is grades are always "middle of the road" in the beginning.) However, the reading levels in our school are cumulative and they like to keep the students all in the same range, which is where such a grade could hurt It could be used as a reason not to instruct her on her true level it that level is "too high" ykwim? That's what they do on my son's school.