volunteer one-on-one help to minority kids who had trouble reading and writing in inner city NYC schools. I was assigned a 5th grader who still did not know all the letters of the alphabet. When I talked to him about it, he told me that if you didn't know the work and caused trouble in your class, you were left back. If you didn't know your work but sat quietly, you graduated to the next grade.
I spent a semester trying to help him but he still did not know all the letters although he was doing better. As an engineering student, I was probably too techy to figure out how to motivate him and approach his problems in a different way. I see now that teachers who know how to deal with such kids can be really successful if they have the backing of the schools. I still feel my failure to recognize that and try to get some help for how best to help him.
If a school doesn't care, the kids suffer. When my oldest was in school, we really pushed them to provide the help he needed (he was a gifted underachiever) and threatened them with filing a complaint with the state education department. Unfortunately many poor parents didn't want to "cause trouble" or don't know how.