Personally, I think social and cultural capital is just as big a determinant of life chances as parental income, but it is harder to study and is more subjective.
Yes, I'm professionally involved in lots of Early Years initiatives myself, and the above is resoundingly true. My parents income was middle class, but my cultural capital means that a lot of people peg my sister and I as privately educated.
Museums, castles, trips to cultural locations, tv mostly adult and literary based, education in Greco-Roman, British and Egyptian mythology, books as gifts, language tutoring, a house with thousands of books, encyclopaedias, parents with four degrees between them (science/computing/history/english, so wide ranged too), calligraphy, riding, membership of geeky clubs - young ornithologists and archaeologists, St John's Ambulance, different geographical environments, science documentaries... all of that, in spades. I didn't bat an eyelid at any sort of concept being introduced at school because I already had the grounding.
If you lack cultural capital, then you start a lesson learning what the seaside is like, rather than dashing off to write a poem about a shell etc.
“They possess relatively more cultural and social capital than their peers, and indeed the very act of participating in the GBCS was a ‘performative’ way of claiming cultural stakes”
Oops! Haha, yes. Pointing out the flaws of a demographic survey is pretty meta in terms of performative MCness itself 