My coworker's wife was a math major. She volunteered to help at her child's public school. (kind of surprised that this is allowed, actually) The teacher gave a math problem, "BLANK - 9 = 9", accepting both 9 and 0 as the only valid answers. My coworker's wife tried to correct this, claiming that 18 should be the only valid answer. The teacher insisted that 18 was incorrect because they hadn't covered 2-digit math yet!!!
This is not any sort of impoverished school, nor is it rural or urban, nor is it significantly non-white or immigrant or anything of the sort. It is borderline wealthy. Statistically, you'd expect it to be nearly the best America has to offer.
Nobody should want an equivalent to that.