It isn't all about money or class and it isn't all about the parents, it's also about society as has been pointed out.
It benefits those at the top to have a mass undereducated population both to do the jobs that they require but don't want to do themselves to maintain their status and comfort as well as to maintain the hierarchical status quo. It's getting to crisis point now with far too many in the educational underclass to fill needed specializations and still they do little but play around the edges of educational and social reform because it benefits
I live in an educational black spot. Of the secondary schools accessible to us, only one gets over half of their students to the basic standard of 5 good GCSEs or equivalents - and that's a selective school with an entrance exam. It does help by taking their first 50% from those in the 5 poorest wards, but it's obviously massively oversubscribed because it's pretty much the only game in town in our inner city. There are a few other 'nice' schools at the edge of the city, but most are quite poor and known more for their violence and self-harm problems (sadly even that best school have had recent reports of horrificly violent bullying). Even more sad is that the services don't expect more or push for more.
My children have had someone whose job it is meant to be to help lift them out of these issues and help parents that are being described (as my kids are young carers who have dealt with bullying and social isolation) and she plain said that bullying was just something everyone has to push through and that the education standards of our area are just what should be expect in this area. She gives far more effort in wanting to get the house redecorated than in dealing with their social isolation and gaining access to community resources. Seriously, she went on about how nice it would be to get the laundry area painted, about new bedding and planting flowers, but try to get her to talk to the kids about their difficulties in the area and how to connect to community resources always gets brushed off. It's become quite upsetting especially to have someone who is meant to helping to improve my kids' chances and lives talk more about the colour of their bedroom walls than my kids' actual concerns and desires for friends and connecting with others. Daft yet typical of what we've dealt with. Doesn't even help with the work, just gives us ridiculous timelines that don't take our disabilities into consideration. Very frustrated with with official help falling apart and causing more pain at the moment.
We say parents should do X, Y, or Z, but society rarely actively encourages these things. It's all about productivity and short-term fixes (like doing up a bedroom), and pushed a million and one things that can do the job better, and the media rarely shows a well functioning family actually doing these things and facing these issues. There is no mirror or window or any real encouragement beyond a finger wag that they should know better or shouldn't have kids in the first place. There is little practical or reflective that support the things that kids need because it's easier to complain and continue the status quo than consider what is actually needed and helping to set up system that make that happen that actually work long term.
My kids are the bottom of the statistical barrel educationally, and yet are as aspirational as any other (far more than I was at their age and I had far more though no educational encouragement). My DS1 wants to built robots and robot suits to help and protect people, DD1 wants to be a doctor (well, a doctor-pilot-artist). They should be able to be able to have a fair crack at trying, but really I don't know if the doors will be open for them to do so. I can only try my best but there are a lot of barriers in place that don't need to be there, but those that benefit from the system as is are not in any rush to help pull them down.