Like I said earlier: I'm not sure what kind of variables you'd like to include within this variance but I'd LOVE to to hear any suggestions.

There are at least two variables he's missing that matter a lot:

(1) Selection bias. The pool of immigrants who make it to America in the first place likely skews well above average.

(2) Culture/ecosystem problems in black communities, even if it's politically incorrect to argue it. Black neighborhoods are plagued by gang culture/violence, drugs, patriarchal absenteeism (estimates vary, but roughly 50% seems likely), intergenerational educational deficit (if parents are illiterate/undereducated, their children are likely to be so as well), and various other more generic issues that stem from chronic poverty.

If the level of absenteeism is very high, it is very likely that the parents are renters and not homeowners, so it circles back a little to the main point.