In the 1960s in the state of New York, public school children started their day by reading aloud a short nondenominational prayer that had been written by the Board of Regents. Eventually, a group of parents sued, arguing that it was unconstitutional for the public schools to sponsor this sort of religious activity.
The Court agreed, saying that school sponsored prayer violates the Establishment Clause of the First Amendment, which guarantees a wall of separation between church and state. This was true even though children were not required to say the prayer. The Court said that New York was advancing religion simply by sponsoring the prayer -- something impermissible in a public school setting.
Engel was the first in a long line of cases in which the Court struggled to clarify when religion is impermissible in a public setting. Another important case in this line was Abington School District v. Schempp, in which the court said that Bible readings were also impermissible in public schools.
370 U.S. 421 (1962)
CERTIORARI TO THE COURT OF APPEALS OF NEW YORK
Because of the prohibition of the First Amendment against the enactment of any law "respecting an establishment of religion," which is made applicable to the States by the Fourteenth Amendment, state officials may not compose an official state prayer and require that it be recited in the public schools of the State at the beginning of each school day -- even if the prayer is denominationally neutral and pupils who wish to do so may remain silent or be excused from the room while the prayer is being recited.
10 N.Y.2d 174, 176 N.E.2d 579, reversed.