I think this quote is a good transition into determining whether school vouchers are good policy:
"It constantly amazes me that defenders of the free market are expected to offer certainty and perfection while government has only to make promises and express good intentions. Many times, for instance, I've heard people say 'A free market is a bad idea because some child somewhere might fall through the cracks,' even though in today's government school[s], millions of children are falling through the cracks every day." -Lawrence Reed
One of my biggest kvetches about the status quo is that for many students, they are limited to public school in which they are districted. Some students can afford private schools (only 11.3% of students are in private schools ), and a small percentage of parents are able to facilitate homeschooling (2.9%, as of 2007). However, most students, especially those from families in a lower socio-economic stratum, do not have those options. Even for those who do opt to get out of public schools, many are double-whammied: once with paying property taxes that go to a public school that their children are not even using, and once to cover the tuition for a private school. For those who are not financially well off, this can be very financially burdensome.
Although the government technically doesn't have a monopoly on education, it still acts as a monopoly because the government really does not face direct competition, which does not incentivize them to improve upon their product. What the school voucher program would do is give parents the option of applying the voucher to a public, private, or parochial school. Creating a competitive market, both in economic theory and in practice (also see here and here), engender overall better quality for a lower price. And in the event that you are worried about there not being specific case studies, how about Washington DC, the city of Milwaukee, the state of Florida, Alberta, or Sweden?
How does school choice engender this sort of change? Because when parents "vote with their feet," they incentivize schools to perform better and hold schools more accountable to maintain expectations. We can see schools be more innovative, such as offer alternative subject matter (e.g., vocational skills in the high school level) or alternative school hours. This sort of competition has already succeeded in the collegiate level where public and private universities compete for GI Bills and Pell Grants.
Since time is not on my side right now, I have to conclude rather than delve into more facets of school vouchers. If we are to implement school vouchers in more places, I worry about the regulatory oversight being burdensome where change and innovation would be stifled. I know it's not a completely liberalized education market. It would be great if it could be, but pragmatism has to step in. Given how slow change happens in American politics, I know gradualism is not only more pragmatic because it wouldn't deliver a shock to the political system, but also because people can handle change in more gradual doses. This is why in spite of imperfections one can find with a school voucher system, I believe it is a step in the right direction. Providing a more competitive market, albeit with government oversight, is better than the status quo, which is why I hope the efforts of National School Choice Week translate into legislation towards a more liberalized education market.