Charter schools, especially in big cities, seem to have performed significantly better than traditional public schools, and some black parents are very aware that their children might be better off there. So all that Tom Sowell is saying is that Republicans running for office who defend charter schools staunchly against far left 'Rat opposition might likely find some critical black votes swinging toward them, enough to make the difference in close elections. As far as that goes, Sowell makes sense.
The sad fact is most of the inner-city parents don't give a damn. Remember the saying about leading a horse to water. Nobody wants to bring up the IQ gap having an enormous impact on the whole thing. It's almost impossible to teach low IQ children who many times are bored and violent. That's the sad situation.
The only person I know who I know has at least one kid in charter school is black; he’s got five kids (that I know of) and making sure they got a good education was a very high priority; he didn’t get that shot when he was that age (and we’re the same age), and grew up in a POS public school system.