Binners happy to accept the serious question.
I think the first challenge we have to overcome is this notion of class. I think everyone can agree what it looks like/means etc when we see the extremes, so the very top echelons contrasted against the very bottom (and it's not universally about money either). But let's not get too into that as it's a whole other thread, more pages than this one.
Let's agree that there is a relatively easily identifiable notion of working class and middle class and then ask how do your recognise which families are which.
I would be saying that the ones where parents encourage their kids to do well, to apply themselves and study hard, where education was critical, formal or otherwise (and I think that education isn't confined to just formal schooling. It can come from other areas such as hobbies or societies for example), where being a contributing member of society was something that should be aspired to, those families would be what I recognise as middle class.
The working class families would be where those values are not just not taught, but where there is also evidence that they are derided.
There were some pretty nasty pieces of work in my class, they were working class than and they're working class now and short of them being a problem for society, that's just how things are.
There were also a lot of kids from families that might have been recognised as working class back then but because of their attitude towards education (formal or otherwise) are now what people would call middle class.
Someone above made the point - mum was a hairdresser and dad was a mechanic but we worked hard at school, went to university and now have pretty good jobs.
That's my point; are they still working class or are they now middle class?
I have seen a lot of evidence of social mobility from my generation; that may be different now but I suspect that education is still the key to social mobility - ironically Binners I think I have talked my argument round to you and I being in wholehearted and violent agreement.