I didn't realise being poor meant you were less intelligent. Being lazy makes you thick, you set your own limitations and no one else
Whilst I somewhat agree with you, when everyone around you is a lazy sod who doesn't give a **** about their future, I'm fairly sure it has some sort of negative effect by osmosis.
As suggested below, I think it probably has a lot more to do with the parents, but even if you're the lone kid with good parents in a school filled with the unwanted, it probably will set you back.
I was a poor kid, my experience was that it was hard to learn in the classes I wasn't so good at because the my peers simply didn't give a toss. They were disruptive, and a pain in the backside, but aruging the point would have simply been painting a target on my back.
So instead, I kept quiet, went to college, then uni, then got a job and worked on a postgrad, and here I am. It hardly ruined my life, but to say it isn't a disadvantage to be in a school which basically doesn't care about teaching you is something I'd need to disagree with.
Many get through it, but enough kids give up on their future just because they don't know what to do about it for it to be considered a real problem, and for it to matter.
Yes being poor is a disadvantage, Yes being in a weak school is a disadvantage. But if you have the willingness to learn and you realise from early on that getting good grades is your ticket out of a poor life then both those things make no difference to how well you do at school. Home not a good environment to study? Go to the library, study there, teachers are rubbish? I had that, taught myself from the text books. Getting 90-100% in tests for Maths and Science, went to a decent uni in London and got myself a Physics degree and a post-grad in Computer Science. There is no reason at all for anyone, any child, not to do what i did and improve their situation.
Getting beat on is a pretty good reason.
I do agree with you that the chances is there for those who want it bad enough, but I still think the situation can be greatly improved from what I was at school.