ANOTHER EDITION OF "BE CAREFUL FOR WHAT YOU ASK FOR"? The Supreme Court has found school vouchers to be constitutional.
I've been a long-time supporter of vouchers, for a ariety of reasons. But, as Prof. Reynolds points out, there is an undeniable likelihood that vouchers will be used to support students' attendance at schools like jihad-loving madrassas.
Jonathan Rauch has pointed out some likely yet unforseen consequences of a wide adoption of school vouchers:

[V]oucher schools won't be unregulated. Taxpayers will demand to know why their money should support any schools that lack certified teachers, that reject affirmative action, that have leaky roofs, that produce low test scores, that duck testing altogether, that ignore special education, that teach only in English, that provide no counseling, that expel students without due process, that turn away too many applicants, that teach goofy curriculums, that shortchange girls' sports, that skimp on antidrug education, that ban gay clubs, that allow gay clubs, that teach too much about sex, or that teach too little about sex.
The public is accustomed to holding schools politically accountable, and to thinking of quality schooling as a right; it will apply both principles to voucher schools, much as it already applies them to health maintenance organizations, and may soon apply them to pharmaceutical companies. Some schools, especially religious ones, will hold out by shunning government money. But their number and market share will dwindle, as billions of taxpayer dollars pour into voucher schools. Over time, the character of American private education will change. Eventually, most private schools may look less like private schools and more like privately owned public utilities.
The qualification is that there would be more competition in education than exists today. Voucher money would seed thousands of new private schools, and public schools would be more competitive. In fact, competition would pressure ossified public schools to cut red tape, even as politics pressured private schools to spin more of it. Because public schools enroll almost 90 percent of the country's pupils, the net effect would almost certainly be positive.
If you happen to be a New Democrat, say, or some other variety of government-friendly pragmatist, vouchers are a great idea. Increased competition in the education sector as a whole will delight you, and the increased regulation of private schools won't bother you much. The Right's unalloyed enthusiasm for vouchers is a bit harder to justify. Conservatives want to get the state out of public education; they may succeed at getting the state into private education. Twenty years from now, they may be slapping their foreheads and saying, "What were we thinking when we crusaded to hook private schools on public money?" And the teachers unions, which by then may have extended many of today's anticompetitive public school rules to the private realm, may be saying, "Boy, were we ever lucky we lost that fight. Now all schools are public."

I think Rauch is correct. It's impossible to take government money and hold out indefinitely against strings, and in general, the trend towards greater federal governmental involvement in education is very strong.