The Arkansas legislature passed a law prohibiting teachers in public or state-supported schools from teaching, or using textbooks that teach, human evolution. Epperson, a public schoolteacher, sued, claiming the law violated her First Amendment right to free speech as well as the Establishment Clause.
Seven members of the Supreme Court agreed that the statute violated the Establishment Clause. Writing for the Court, Justice Fortas wrote, “The State’s undoubted right to prescribe the curriculum for its public schools does not carry with it the right to prohibit, on pain of criminal penalty, the teaching of a scientific theory or doctrine where that prohibition is based upon reasons that violate the First Amendment.”
He further wrote that the government “may not be hostile to any religion or to the advocacy of no-religion; and it may not aid, foster, or promote one religion or religious theory against another or even against the militant opposite.”