The relationship between religion and government in the United States is governed by the First Amendment to the Constitution, which the Supreme Court has held both prevents the government from establishing religion and protects privately initiated religious expression and activities from government interference and discrimination.
Since 1995, the U.S. Department of Education has published and periodically updated
guidance on religious expression in public schools.
Guidance for educators on religious expression
Religious Expression in Public Schools: Staff Discussion Guide
Guidance for students on religious expression
Religious Expression in Public Schools: Student Discussion Guide