There's a difference between knowing how well you're doing, and having that compared to everyone else for all to see (and yes, I remember GCSE results being posted for all to see)
Put it this way. DS is pretty average academically. Last year, for one term, he had a teacher who compared him to other kids, did that thing where they exchange tests to mark each other (tricky when your handwriting is as bad as his was - he's now diagnosed, she said nothing was wrong with him, he was just immature and not trying hard enough), continuously picked on him for not understanding stuff (new school, new country, new teaching schemes - and he was bloody 6, so yes, sometimes he didn't understand). By the end of that term of torture, he was barely speaking in class, and hated school.
One term of a more positive teacher, and he was back to his old self. One term of being praised for his effort and attainment rather than that compared to the others, and you couldn't hold him back - he's getting As now, proudly read out his whole Christmas report, can't wait to get to school, is fully involved in his class.
I on the other hand was a high achiever at school, I always knew which maths book my rivals were on. A wall chart would have just given me more to pressure myself with - it wouldn't have been good for me either!
You could say he's a special snowflake, but then, aren't all kids different? Why on earth are we comparing them like they're all supposed to be identikit kids reaching the same standards at the same times? If there's comparison, it should be for their personal benefit, not used as a bat to beat them with.