Vouchers for untested schools?

Statements like "“Promise Scholarships” would average $4,000 and allow students whose public schools have failed to make adequate yearly progress for five years in a row to attend private school." from a Hoover Institution report contain a hidden premise: that a private school must be a quality school. There is no such guarantee. The only thing a private school guarantees is to keep its customers happy, and anyone who teaches knows that there are a lot of customers who are much more interested in the credential or the grade than in any of the learning that is supposed to be behind it.

In my role as a faculty member, I help advise incoming students. I see plenty of examples of students from small private schools who join the products of our (justifiably) failing public schools by placing into the 5th grade arithmetic "prep" class.

As the Chronicle reports, the NCAA, having banned any HS credits from at least 15 prep schools, has now acted to limit student athletes to only one course from "prep" schools. Clearly they see a problem with the competition between profit and quality.

If a public school must meet specific content, testing, and progress benchmarks to keep its funding, why shouldn't a private school meet those same requirements to get that same public funding? What are they afraid of? Two guesses and the first does not count.