I haven't read the entire thread, but I used to date a 5th grade teacher working for a metro area school. She would tell me on average, she'd have 4-5 kids a year in her class of around 20 that read at a 1st or 2nd grade level. And because the process was so difficult to actually hold the kid back to work on his education, the kids would be moved up the next grade. So, I can see his point where his elementary school teachers failed him. However, it sounds like it's more a systematic issue where teachers feel it's too difficult to hold kids back to repeat a grade, and instead just push the kid to the next grade level.
To reply to that, I have taught at an extremely low socio-economic school.
It's not hard for the teacher to say this kid should stay back, or this could should move up. It's hard to get the parent to agree. That's the hard part. The Teacher only "moves the kid up" because that's what the parent wants to do. I've never heard of a school district that can force a parent to make their kid stay back a grade. They can only make strong recommendations...
So once again, that's on the parent, if that's truly what the issue is. NOT THE ELEMENTARY TEACHER FOR CRYING OUT LOUD.