And I'll add that, for the lower end of the SES and academic achievement spectrum, which does overlap disproportionately with less-involved parents (making no judgement on why they are less-involved), there is a decent amount of research suggesting that involving those students in organized team sports has beneficial effects on their academic achievement and other positive life outcomes. For those children, sport is a way of helping them stay engaged in school and their futures.
Exactly why I don't think school sport teams should exclude children, definitely rank teams in order of ability if need be, but don't only have the a and b teams. I was useless at sport but I really enjoyed it at school.
Also the whole sports thing is rampant in Australia and NZ, I'm sure Puffin and Squishy can back me up here. The All Blacks currently in Chicago are gods here - if you don't have some interest in rugby you really are on the outer - unless you are a women, of course - there's netball for the ladies..... At least in the US you have a range of sports that are social currency.
