Mueller v. Allen

The Mueller decision spelled out the way states could help parents who sent their children to private schools, by allowing tax breaks apply to everyone. However, the dissenters in Mueller thought the decision ignored the true effect of Minnesota tax law: the subsidization of religious instruction. In his dissent, Justice Marshall opined that the Establishment Clause applied whether a subsidy for sectarian schooling was direct, as in Nyquist, or indirect, as in this case. Unlike Rehnquist, Marshall was influenced by the petitioners, statistics, and he concluded that they revealed the failure of the Minnesota tax law in the second part of the Lemon test. By almost exclusively helping parents who paid tuition for parochial schools, the tax did advance religion.

Marshall summed up his discomfort with the majority opinion:

For the first time, the Court has upheld financial support for religious schools without any reason at all to assume that the support will be directed to the secular function of those schools and will not be used to support religious instruction. This result is flatly at odds with the fundamental principle that a State may provide no financial support whatsoever to promote religion.

Previously, the Court had allowed states to fund parochial schools for non-religious obligations and activities, but nothing that was specifically religious. The Court upheld that standard two years later in Aguilar v. Felton.