He said, she said
I call it a case study because it's a perfect example of the pitfalls of subjective grading, which I previously wrote about here. We have no independent data to use in determining who's right and who's wrong. Are the kids skilled at math, and the teacher is grading them unfairly? Are the kids not putting in the effort? Is she a bad teacher? Is she trying to push them harder than other teachers? Is she a hero or a villain? We have no way to know - there's no objective data to work with, no independent evaluation with which to anchor this argument.
Those who responded to my original post have noted the logistical challenges of establishing fair and independent evaluation. And of course they're right - it would be a major undertaking. But if you're this teacher, and assuming you're in the right, wouldn't you want to have that kind of third-party data handy when you meet with the school board? And multiplying this case hundreds of thousands of times over across the country, wouldn't we have a better education system if we separated instruction and evaluation to generate valid information on learning, as opposed to the conflict-of-interest-laden model we have today?
Yes, there are challenges to establishing fair and independent evaluation - but things are only truly impossible when we don't want to do them in the first place.