Lemon v. Kurtzman [Alton J. Lemon, et al v David H. Kurtzman, Superintendent of Public Instruction of Pennsylvania, et al. John R. Earley, et al v. John DiCenso, et al. William P. Robinson, Jr. v. John DiCenso, et al.]
Before the Supreme Court of the United States 403 U.S. 602 (1971), Chief Justice Warren Burger, presiding
Argued: March 3, 1971
Decided: June 28, 1971
Vote: 8-1. Majority by: Burger joined by seven justices (8-0 in Rhode Island and 8-1 in Pennsylvania)
Dissent by: White
Ruling: Held. For a law to be considered constitutional under the Establishment Clause of the First Amendment, the law must have a legitimate secular purpose, must not have the primary effort of either advancing or inhibiting religion, and must not result in an excessive entanglement of government and religion. If any of these three prongs is violated, the government’s action is deemed unconstitutional under the Establishment Clause of the United States Constitution.
Background:
The case dealt with Rhode Island and Pennsylvania programs that 
supplemented the salaries of teachers in religiously based private schools for teaching secular subjects. The cases were bundled together. Rhode Island provided for a 15% salary supplement to be paid to teachers in nonpublic schools at which the average per-pupil expenditure on secular education is below the average in public schools. Eligible teachers were required to teach only courses offered in the public schools, using only materials used in public schools, and must agree not to teach courses in religion. Pennsylvania’s law authorized the state Superintendent of Instruction to purchase certain secular educational services from nonpublic schools, directly reimbursing those schools solely for teachers’ salaries, textbooks, and instructional materials. Reimbursement was restricted to courses in specific secular subjects, the textbooks and materials must be approved by the Superintendent, and no payment is to be made for any course containing any subject matter expressing religious teaching, or the morals or forms of worship of any sect. The concern of the Court was that the two states’ policies could result in the states having to have detailed and complicated financial and other dealings with parochial schools thus violating the entanglement prong of the Lemon test.
What came to be known as the Lemon test is to determine when a law has the effect of establishing religion. While the case and the test do not relate directly to the teaching of evolution, they have significant direct effect on future cases. Even if a scientific theory like evolution expressly goes against a religious belief, teaching just that theory and not the opposing belief does not violate the neutrality requirement of the Establishment Clause. Teaching science has a clearly secular purpose, and is not primarily designed to undermine religion. Any undermining of religion by science is an incidental, not primary effect. It would–under the Lemon test–be unconstitutional to teach a theory whose primary intent or effect was to undermine or to promote religion.
Consequences:
Despite considerable concern and public argument by critics, including recognized Constitutional scholars, the Lemon test has been successfully used in multiple cases of evolution vs scientific creationism or intelligent design. However, the SCOTUS did not hear a case directly involving the teaching of creationism until Edwards v. Aguillard in 1987.