One can make this about whether school vouchers work or the economic practability of such vouchers. Obviously, being libertarian, the ideal country would be one in which the government would not have to tax for education, especially considering that it is not a public good. However, if we live in a world where such taxation exists, I would much rather have it reappropriated to the taxpayers. That way, it creates competition with the public school system, which now gives the public school system incentive to improve upon itself. Also, it gives the taxpayer more say as to where his money is used.
My brief on this issue will be brief. In order to figure out the constitutionality of school vouchers, one has to know what a school voucher is. In essence, a school voucher is a certificate issued by the government to help offset costs if they so choose to send their child(ren) to a private school. In short, a school voucher reallocates tax dollars back to the taxpayer in order to bring a more level playing field in the choice between public and private school. If a parent does decide to send their child to private school, they still have to pay taxes for public school. This description should make the answer a bit self-evident. The government is giving the money to the taxpayer and saying, "Apply it to whichever school you like, whether it would be religious or secular." The act neither establishes nor endores a specific religion. Therefore, the answer must be that school vouchers do not violate the Establishment Clause. This is the exact same thought process that the Supreme Court thought when it decided on Zelman v. Simon Harris (2002), the Supreme Court case which stated that school vouchers are constitutional. Since the aid was not direct, the aid was thereby constitutional, much like it was in Everson v. Board of Education (1947).