Yip that is a big part of it. I remember a black academic in the USA who done a study on why black students on average were getting lower marks than their fellow white students even though they had the same facilities and their parents were equally middle class. He looked at absolutely everything trying to figure it out, and at the end of the day found that the black parents for whatever reason were not participating as much in the development of the child after school. They weren't following up as much, discussing the school day, enforcing strict completion of homework each and every day, etc. In a sense their attitude was that they were paying the school to teach their kids, and thus had doing their job.
I'm not in any way trying to bring race into it, i'm just saying when parents don't play a role, for whatever reason, the kids don't do nearly as well. So much of it is about a culture of excellence, and that starts at home.