The Sloan v. Lemon case in 1972 revolved around a Pennsylvania statute that provided reimbursement to parents for expenses incurred from sending their children to nonpublic schools, including religious ones. The Supreme Court ruled the law unconstitutional as it violated the Establishment Clause of the First Amendment by providing direct and substantial aid to religious institutions. The court found that although the law was ostensibly neutral towards religion, its primary effect advanced religion because most of the benefits flowed to parochial schools. This decision reaffirmed previous rulings which held that government cannot use taxpayer money to support religious activities or institutions, maintaining a clear separation between church and state.

In the dissenting opinion for Sloan v. Lemon, Justice William O. Douglas argued that the Pennsylvania statute in question did not violate the Establishment Clause of the First Amendment as it didn't promote a particular religion or favor one over another. He contended that providing financial aid to parents who chose to send their children to nonpublic schools was simply an effort by the state government to ensure all children received quality education regardless of their school choice. The law, according to him, aimed at benefiting students and parents rather than religious institutions themselves; therefore, it should be seen as secular and permissible under constitutional scrutiny. Furthermore, he emphasized that denying such assistance could potentially infringe upon free exercise rights of those choosing religious schooling for their kids.