I think it expectations and attitude towards education including value placed on it.
I think that starts with expectation that you talk to very young DC.
I'm in a deprived area and was always surprised the number of parents happy to talk to my young DC and ignore their own non verbal DC - in fact I was in one case told it wasn't worth talking to this DC - yet he made noises and pointed and communicated about toys to me.
I also surprised in DH home town and here the number of parents who think education is solely the schools responsibility - so know an area their DC is struggling in tell the teachers and that it their part done. Not how do we help - or actively looking for stuff.
MIL isn't well educated or particularly keen on education past a point - yet she talked to DH, took him to library got involved in his projects - FIL emphases benefits on non-manual labour career and he's educated to PhD level. My parents did similar - though it was my Mum placing the value for her daughter on education and interestingly it us who’ve got degrees and post graduate qualifications but didn't to her DS who in min wage job.
To us this is parenting getting involved and encouraging little projects and interests - yet one of our DC teachers praised us for doing it - and kept on to that DC how lucky they were we did.
Our parents got us past low expectations from educational people - as we have with our DS. The area we are in has low expectations of boys - we had to work with DS at home to show him he could do things.
I expect parents who rarely see their DC but are highly educated mange to convey the high expectations and a good work ethic to their DC - and would be more likely to intervene with either time of money when the DC hit problems.
I do concede minifingers has a point – you can do everything right and the DC can still have no interest and no motivation.
I think the number of books is probably now out dated. They used to be main source of information - but these days with internet or even with iplayers and things like sky boxes making it easier to search for relevant tv programs – having access to information is less about books these days.