That was a brilliant post at 15.40 violethill
usualsuspect no-one is assuming that all middle class children are bright, that they don't coast, that they don't smoke weed, but as Sakura said earlier, one way or another, statistics show that they do 'alright' in the end, in spite of their comparative failings, so who is terribly concerned about them anyway?
If a few of them are flailing around without direction or hope of betterment, subsisting on a minimum wage or benefits - tough. That's 'equality' in action for you. They had all their chances on a plate when they were born into relative affluence, didn't they? And they blew it. I'm sure that delights you no end.
But statistically there are not too many of those, are there? Or at least if there are, no-one is collating figures on them, and saying that they have been unduly 'disadvantaged' by the unrealistically high expectations of their middle-class parents, and the pressure to succeed. 
usualsuspect You say that people have a stereotypical attitude to 'the poor' and nothing will change while people think that way. But no-one walks into a job interview with 'POOR' tattooed across their head. They may (just may) look poor, sound poor, talk poor. But they may not think poor. Most employers are not stupid - they know intellectual spark and potential when they see it, and provided a young person has good communication skills and a bit of gumption they will be given a chance. People either come across well - or they don't. And that is the same for all people of all classes.
Of course some people will always get a foot in the door of a top career through nepotism, or having the name of a very famous school on their CV, but not many really - not in the great scheme of things. And if they walk into an interview at a decent university the admissions people will know thier circumstances in advance, and all sorts of positive discrimination will have been applied to get them that far (if their A levels are slightly below par in comparison to the rich kids) and they will get a place - if they warrant it.
What irks you, and Sakura and Edam, is the simple fact that a relatively small percentage of working class children are daring to aim to high in the first place, or seem even seem capable of it. 'There has to be a reason!' I hear you shout. 'It cannot possibly be that they just are not as bright as middle class kids! There must be foul play!'
Maybe they are just as bright - but maybe they just don't fancy or value the academic route but prefer to achieve through entrepreneurial ventures? Maybe they prefer to go into trade and work they way up to affluence that way, which is something many middle-class kids are discouraged from doing (and upper middle-class kids positively banned from.)
There are plenty of well educated highly intelligent people who are not especially affluent - not by a long long way, so why should it be assumed that the only way to make a decent living is through higher education?
Of course the poor but bright children who perform very well at A level can go on to secure good uni places, and good jobs, but you won't be happy until every poor child has performed well in higher education, and it can be proven on a graph that they are all performing equally or better than children born into 'advantage.' Because in your world, there is no such thing as inherent intellectual advantage, no limits to the intellectual ability of anyone who is poor,(but the rich can be as thick as they like - just lucky) no good parenting advantage, no advantage gained through encouragement or good example, and no concept of personal drive and ambition.
No, there is only unfair financial advantage. Which means the ability of a pushy hardcore of rich parents to unfairly jump the queue by somehow 'buying' a golden future for their child - a guarantee of a highly paid job irrespective of their ability or drive. Honestly - do you actually realise what a tiny tiny minority of people that actually applies to?
And then in contrast there is the inability to 'buy' it, therefore consigning all poor children to a life of poverty and servitude.
I'm sorry to have to say this, but what blinkered idealistic tosh.
I hear an awful lot of carping about how rich parents with sharp elbows hinder poor kids' chances, but I don't hear much contructive talk about how we stop them. Or how we encourage apathetic parents to value education and encourage their children to aim higher and stick at it. Just loads of blame, and no solutions.