Lemon v. Kurtzman, 403 U.S. 602 (1971), was a case in which the Supreme Court of the United States ruled that Pennsylvania's 1968 Nonpublic Elementary and Secondary Education Act, which allowed the state Superintendent of Public Instruction to reimburse nonpublic schools (most of which were Catholic) for the salaries of teachers who taught secular material in these nonpublic schools, secular textbooks and secular instructional materials, violated the Establishment Clause of the First Amendment. The decision also upheld a decision of the First Circuit, which had struck down the Rhode Island Salary Supplement Act providing state funds to supplement salaries at nonpublic elementary schools by 15%. As in Pennsylvania, most of these funds were spent on Catholic schools.
Read more about Lemon V. Kurtzman: Lemon Test, Recent Use