The biggest thing in school privatization right now is not vouchers. It is charter schools. These are schools which are constructed from scratch by non-governmental organizations, both for-profit and non-profit. There are many more students in these than in voucher systems or in privately-managed public schools. There are hundreds of charter schools, some operated by NEA members. (The NEA is on record in favor of charters.)
Voucher systems are intensely contested, but not very prevalent as yet. These are naturally limited, and always will be. The reason is that students living in higher-income areas will always have first dibs on their superior, local schools. This restricts the intake of non-local students. The other factor restricting the outflow of students from bad schools to good ones is the natural proclivity of most parents, for good and bad reasons, to choose a local school.
It is true that the size of vouchers is likely to be too limited to be worth much. That aside, the logic of vouchers is towards inequality. Higher-income parents will find ways to supplement their vouchers with personal income, and their schools will help them do so. The line between voucher and tax deduction is sufficiently thin to make that outcome more likely as well. Both move us closer towards a pure, individualized cash system -- the bane of equality.
A great unmentioned factor in school quality which nobody has mentioned is the income of the student body's families. More flexibility means poor(er) families chase richer ones. In the end, no more than a minority of parents will want to play this game, as noted above. The sad truth is that parents bear a significant share of blame for their children's lack of educational attainment. Ask why a parent or parents, even low-income ones, could let a year go by without speaking to their childrens' teacher(s). If you doubt this, ask any teacher. And that effort pales before that required to read to a child on a regular basis.
The dilemma felt by concerned parents whose children are obliged to go to bad schools is real and justified. The polling evidence re: minority acceptance of vouchers is overwhelming. Whatever the number of such parents, there are probably not enough places for their kids to go, even with large vouchers. Formation of sufficient private schools to take these kids, assuming the vouchers were available, would take a while. Meanwhile, the drain of funds implied by vouchers will drive the remaining public schools further down.
Magnet schools and programs are a way to sort out students (i.e., allow some parents to separate their children from those of other parents) without moving or paying private school tuition.
My daughter is in a magnet program -- French immersion. Our county -- probably among the top ten richest in the U.S. -- has a handful of really really good schools, where the rich people live, and many others of varying quality. It gets by with about eight magnet programs. This suggests to me that a lot of parents don't care enough about their kids' education to demand a magnet.
Personally I couldn't care less if my daughter is able to read Balzac when she grows up. But she is getting a more rigorous education. Self-segregation was not my wife's motivation for wanting her in a magnet (I had a modest, advisory role), but the result is plain and ubiquitous enough. There are clearly fewer minority kids in the magnet program than in the school as a whole. We were disappointed about this, but not enough to give up on the magnet.
How to fix this? I'll have to pass on elaboration of my school reform program, but a few unmentioned points: there's lots of evidence of non-school factors affecting school performance, mundane things like nutrition, adequate housing, etc. All the burden should not be put on schools. Then there's the work time issue. Parents would and could do a lot more for their kids with shorter work weeks, again a non-school factor.
Finally, re commercialization in schools, it is not at all obvious that private schools are or will be more commercialized. See Alex Molnar's book "Giving Kids the Business." A broad assortment of corporate vendors are deluging public schools with commercialization options. The reason should be obvious: public schools need the money. So they let vendors sell junk food to students, put up advertisements, pipe in "Channel One" rubbish, etc. Parents with a choice of schools could prove less amenable to a commercialized environment.