most of the poor here still is relatively much better off than those from under-developed countries, plus our school provides free lunch, many programs will waive fees if you're economically disadvantaged, etc. It's not as good as those well-off families but it's really good enough for you to do fine in education.
I saw so many economically challenged kids carrying new iphones, dressed well, yet not really into learning at schools, it's certainly not just an economic problem.
Education wise, middle class in a developing or under developed country will still beat poor in a developed country even if the latter have more money than the former. Culture has a lot to do with it, a lot has to do with the latter's parents not teaching current parents the same thing that the former's were taught. Home situation is much of the problem, and you can't just throw money at the problem, unfortunately.
European countries might do a better job at this by either (a) having less poor people (immigrants) or (b) putting in more resources to ensure that these kids get more support at home and in school to make up for their disadvantage. But often, you'll find in European countries that they have the same problems with kids from disadvantaged background being behind middle class kids, they just work at solving the problem better than we do in the states.
Whatever is happening in public schools, you'd do well to increase your child's odds by putting them into something else if you can afford it.
Private school, tutoring, homeschooling, college (dual-enrollment), etc..