Poor kids do have opportunities. Going through the Detroit Public School system myself I seen most kids ignore them.
I agree that the slow learners can get and obtain high achievements in life. But they have to do it usually at a slower pace to get there. While other kids just get it, naturally gifted kids that understand things faster. The faster learners should not be held back by the slower learners. On the other side of the coin the slow learners shouldn't feel dumb by not being able to keep up with everyone else.
To me it makes sense to split these type of kids up so they can get the right education and attention they need based on how well they learn.
Poor kids do have opportunities, but seldom much motivation. This is a prosperous country, and your typical poor kid is usually being raised by a single mother or single grandparent, often addicted to drugs and alcohol. He probably goes to school without breakfast after having stayed up late due to lack of supervision, so he's both hungry and sleepy. Neither is conducive to learning. No one he knows works using the subjects he is supposedly learning - large numbers don't work at all and still receive checks, some work at menial jobs, the more prosperous ones work for the government, and most prosperous are probably criminals. The people he looks up to are probably athletes or actors, because although we claim as a society to respect education, intelligence and achievement, the people we glorify are mostly athletes and actors. The scuzziest, least intelligent people imaginable he sees with their own reality shows, and if he sees anything at all about science, it's probably a super villain or blowing up something.
His friends probably don't value academics either. His one parent or grandparent is probably either apathetic due to addiction, or too tired to exert much discipline. She is also probably highly protective of him, or more properly his prerogatives and his cred, much more likely to protest a teacher "dissin" him than to protest his acting out or failing to show up.
Single parents and the welfare state have absolutely destroyed our culture with regards to education, but this is the population we have to work with. We'll always have some kids who are smart enough to self-motivate in the worst situations and some single or poor parents who manage to make their children work for their future, but most kids are by definition, average. In this kind of situation, most kids will fail. If we are to not fall into Third World socioeconomic status, we have to motivate at least most of these kids and their parents to excel.