Here are a list of precedents for the case.
Lemon v. Kurtzman (1971): A government action must: 1)relect a clearly secular purpose, 2)have a primary effect that neither advances nor inhibits religion, and 3)avoid excessive government entaglement with religion.
Cornelius v. NAACP Legal Defense (1985): The school district, like the private owner of property, may legally preserve the property under its control for the use to which it is dedicated.
City Council of Los Angeles v. Taxpayers for Vincent (1984): The First Amenmdent forbids the government to regulate speech in ways that favor some viewpoints or ideas at the expense of others.
Widmar v. Vincent (1981): The Court suggested that the interest of the State in avoiding an Establishment Clause violation may be a compelling one justifying an abridgment of free speech otherwise protected by the First Amendment, but permitting use of university property for religious purposes under the open access poilcy involved there would not be incompatible with the Court's Establishment Clause cases.