It's not a trick question. A logical outcome of a voucher program is that the public school system becomes a remedial academy of sorts. This isn't necessarily a bad thing as the problem becomes too stark to ignore. It is the inverse of NCLB-meets-inclusion where every classroom becomes a one-size-fits-all environment and everybody loses. The hurdle to be faced is that public school classrooms will be 92.4% minority, 96.2% poor, and the race pimps and their ilk will have a major cow.
I believe the Louisiana legislature, governor, and Supreme Court have told them, in advance, what they can do with their cow.
As a real suggestion, perhaps the state, or individual districts/parishes, could pass a "sunset date" for the public school system. After that date, anyone who was not using the voucher to pay for education would be considered neglectful, and the children could be placed in apprenticeship programs, if appropriate, or directed into a suitable private school. There could be a "default option," taking into account the needs of individual students, for those children whose parents refused to choose a schooling option themselves.
Public schools in poor urban areas will tend to be those that are worst off - it’ll be those predominantly poor minority parents who are most likely to try and get their kids out of the failing system.