Note that persons on both sides of the question favor public education. The difficult question is whether funds should be diverted from public schools in order to fund education at private schools. The question is acute, because in the U.S., many unaccredited public schools have per-student costs more than twice the tuition of accredited private schools in the same area. In many areas, the accredited private schools also have superior educational outcomes.
The economic theory in favor of "educational choice" is that parents and students are strongly concerned with the quality of education received by students. Therefore, if given a choice, they will seek out the best educational institution they can afford. Tax credits would enable tax payers to have more educational options. Vouchers would extend this choice to the poorest members of society by subsidizing their choices with public money that would have gone to public schools. A mild form of school choice, with increasingly wide endorsement, is to provide parents with choices between various public schools.
The advantages to society are supposed to be several. First, people will be as well educated as possible. In particular, vouchers might easily help equalize educational outcomes for underprivileged children and middle-class children. Second, that the available money for education should theoretically tend to flow to the best available learning methods, and institutions and possibly even save a lot of money.
The primary criticism is that diverting money from public schools cannot make them better. Most people in the U.S. also want to be sure than the public gets its money's worth. Critics charge that the assumptions are false: It is said that neither parents nor children are qualified to evaluate educational systems. Also, critics say that commercial schools will be organized for maximum profit, rather than for most effective learning, and therefore the costs will be high, and the education no better than existing public schools. Furthermore, parents who have more of an interest in the success of their children's education are essentially trying to push their children out of the 'poor apathetic class' into the 'middle class'. Critics suggest that voucher based schools is an efficient way of further separating the classes.
These concerns are met by providing choice between public schools. However most school choice activists want more. They specifically want non-governmental schools included in the choices, often to obtain religious instruction.
This leads to a further discussion concerning whether it is moral to force people of one religion to fund (via taxes and redistribution) education in another religion's schools. It turns out that a large majority of parents favor this, whether or not they think it is legally possible. (See reference at the end.)
Most persons consider a tax credit for private education to be morally acceptable, because the money comes from the parents' taxes. In the U.S., this argument has been accepted by federal judges, and is law.
In the U.S., the legal and moral precedents for vouchers may have been set by the G.I. bill, which includes a voucher program for university-level education of veterans. The G.I. bill permits veterans to take their educational benefits at religious schools, an extremely divisive issue when applied to primary and secondary schools. Voucher systems for primary schools have also quietly operated in some New Hampshire school districts since education became mandatory in the 19th century.
The political lines are drawn between several groups:
Public teachers' unions are implacable foes of vouchers, and only reluctantly accepting other forms of school choice. They also contribute large amounts to politicians. This is believed to be because the unions would face great losses of membership were vouchers to become universal. It is both fair and accurate to say that many public schools appear to be doing an adequate job.
Most middle-class parents are mildly satisfied with their public schools, but think that private schools would be better. Many of these people chose their residence based on the quality of schools, and so have already engaged in an expensive form of school choice.
There is a small coterie of libertarians that originated and strongly support vouchers with a miniumum of public regulation, however they are a tiny, politically-impotent minority of the public.
Inner-city parents without such options and with underperforming schools are dissatisified with their schools, but many also have lowered expectations, and considerable apathy. A growing number of inner city parents are pushing for vouchers, with regulated schools, for underprivileged children, as a workable educational reform. In many areas, wealthy persons are funding private voucher programs as opening wedges, demonstration projects intended to prove that school choice works. Early returns indicate that these improve outcomes, though not as well as reformers had hoped.
Liberal political elites divide into politicans, and citizen activists such as the NAACP. These agree in theory that vouchers would not increase democratic instutitions. However the activists are coming under direct and increasing pressure from their traditional constiuencies, who are forming organizations such as Black Advocates for Educational Choice (BAEC). If the current trend continues, the politicians will almost certainly have to follow these broad-based groups when they change direction, and accept vouchers as an equity-inducing institution. Ultimately, politicians need votes, not money.
If and when this break occurs, teachers' unions will lose much of their influence, and voucher systems of particular sorts will become more likely to be implemented as legislation.
Trends seem to indicate that vouchers in the U.S. for underprivileged children will arrive at many places sooner than for the middle class. Also, these programs are likely to have substantial regulations on schools, and be justified by concerns for an equitable education. They are likely to be viewed as experiments, and justified by the results of experiments with private vouchers.
After these limited programs have been established for some time, and society has sufficient confidence, then the experiment may be extended to the middle class. If the courts prevent full voucher programs, then limited ones using tax credits might still come into being. Tax credits have already been tested in U.S. courts, and would provide sufficient incentives to move many more children into private schools.
For more details, including statistical research supporting these trends and conclusions, see "Schools, Vouchers, and the American Public" by Terry M. Moe (http://www.amazon.com/exec/obidos/ASIN/0815758081/102-7684998-5888947).