Stan asks, "Why shouldn't there be a market for public education?" and motivates his question with an interesting article from The Washington Post. I would rephrase the question as I have done in the title and try to answer it as follows.<!--break-->
The source of funding, at least to a level of an adequate education for all students, should be public. Education cannot be the way to break the intergenerational transmission of poverty and low income if those from disadvantaged backgrounds get trapped in substandard schools. The cost of properly educating students from disadvantaged backgrounds is higher than for other students. There should be some redistribution inherent in the funding of public education, even if market-based elements are introduced.
The use of the funds, when deciding among a set of accredited providers, should not be publicly controlled. Families should have the opportunity to spend the money that would be allocated to their childrens' education at any school, whether public or private, that is certified and willing to do so. The example in the Post story is an example of how a family with the means to do so is simply foregoing its claim on D.C. funds and paying all of it out of pocket. This makes it too difficult--there should be some amount (even if not the whole amount) of the expenditures that would have been made on the family's daughter that is now available to help pay the tuition at the school in Maryland. If that were the policy, then more students and those from less advantaged backgrounds would have the same sorts of opportunities.
Money should follow the student rather than be paid directly to the provider. Once you have that, good things about a market can follow, without abandoning a core commitment to funding an adequate education for every student.
For more of my views on education reform, see this earlier post.