Why did Engel v. Vitale rule that voluntary prayer in public schools violated the establishment clause?

In Engel v. Vitale (1962), the U.S. Supreme Court ruled that the state of New York’s practice of authorizing a voluntary, nondenominational prayer in public schools violated the Establishment Clause of the First Amendment.1

The Court held that by using the public school system to encourage the recitation of the Regents’ prayer, the state had adopted a practice that was inconsistent with the constitutional prohibition against state-sponsored religion. The majority opinion, written by Justice Hugo L. Black, emphasized that the government may not use the machinery of the state to promote or practice religious beliefs.12

Although proponents argued that the prayer was constitutional because it was voluntary, the Court later clarified in School District of Abington Township v. Schempp (1963) that the voluntary nature of such exercises does not provide a defense against a claim of unconstitutionality under the Establishment Clause. The ruling established that the government must remain neutral, ensuring that public institutions do not advance or inhibit religion.2