I still think of my sons' primary teachers as great teachers, don't get me wrong - but I can quickly count the pics on the wall displays for different topics when am in there and put it this way, there's 30 kids in their classes - but maybe only ever 15-20 bits of work, per display board.
And the way I was trained has a downside - kids who really struggle with art or handwriting or something that affects their presentation, often don't want their work on display. You have to really big them up, and encourage them, and make the other kids too start to see it as normal that everyone's work is up and not to comment or be bitchy if some of it looks, to their eyes, 'bad' (and let's not forget kids are hugely judgmental). I'd find a way to present the work, so no one person's stood out, so for example when they did self portraits in paint, we displayed them by making a giant cut out painting of a bus and just cut out and crowded all the heads on. That way the less great ones didn't stand out.
I was also trained never to put a single thing on the wall the kids didn't do themselves. You'd be amazed how many teachers/TAs still to this day, will 'just do the outlines' or 'help' them so heavily if it's for display, that the kids' have little input. I can always spot a bit of TA or teacher artwork on the walls, and have seen it most places. So the wall is never the place to look for a cue about your child's achievement.
And although we are meant to be PC and only compete against ourselves - which I agree with - on the other hand, you can only get a general sense of where a child is, in relation to others.