I think there’s an extent to which OP is experiencing a modern incarnation of “clogs to clogs in three generations”. It’s very common at present due to a number of societal upheavals.
Our parents generation grew up in the post-war era. There were fewer men, competing for more jobs, so wages were higher and house prices were lower. There were moves in society towards a welfare state, which benefited the poor more than the rich and removed some of the more extreme effects of inequality. One way or another, for our generation, there was a lot more social mobility than there had been before that.
I didn’t go to private school, but had a good stable upbringing (with a mother who could afford to stay at home and run the house) and went into a profession that my father might have dreamed about entering, but almost certainly wouldn’t have achieved. I once asked my mother why dad hadn’t made any attempt to go into my line of work and she answered that it wouldn’t even have been considered a possibility “for people like us”.
I married a man, whose parents had been similarly mobile, from very working class beginnings to very comfortably-off middle class. He did go to a private school.
Because house prices had risen so far by the time we had children, we couldn’t afford private school in the early days. Our children went to a good school initially, but then a much worse one later, where they started to fail. Because we both had to work, I wasn’t there to support them, as my mother had been.
So rather than having children who achieved at school, as I had done, I have children who have done moderately well. And as we all know, a moderately good degree in the UK doesn’t really shift you far up the career ladder.
I think the private school is a red herring. I have sympathy, OP. I had assumed my children would have the same path and opportunities as I did, and unfortunately that’s not looking likely. I have also wondered whether I have failed my children, but I am gradually moving towards the opinion that it’s largely society that has done that. We are moving back into a situation where there are a super-rich elite, and where those at the other end of the scale are far more likely to have insecure jobs and fewer rights than we would have had, even if we hadn’t achieved so well at school.
Those in my once-stable and well respected profession are now experiencing astonishing levels of stress and there is much discussion over whether the future is going to be tenable at all, in its current form.
This is a time of massive social upheaval. I hope that at some point things will change, but in the meantime, I think we have to support our children as best we can, and though you feel you have failed them, OP, you’re probably in a better position than many to do that.
Don’t beat yourself up. You can only do the best you can, so if you’ve done that, then what is happening at the moment is not your fault. There are some on this thread whose children performed as expected, so they perhaps don’t see what’s happening as clearly, but there are a whole generation of young people going out into a world that is much less stable and more difficult to navigate than it was when we left school. Back then, leaving school with sub-par grades could still lead to a stable and meaningful job, which in our parents time would have given opportunities to end up comfortably off. We can only hope that the pendulum will start to swing back at some point, but it might take a major upheaval on the scale of the war for it to begin.