Not an expert on this, but it seems to me that the parent[s] are the crucial factor in success.

The parents who are the most engaged go through the effort to get their kids into the charter school. The kids then succeed relative to the kids with no family structure who are left behind. Was it the charter school that contributed to the success, or was it the parental engagement? I think it is the latter, mostly.

A frank discussion on this would require that we be allowed to talk about the family crisis in inner cities without being labeled racists.