Creationism and the Law
Legal challenges to anti-evolutionist policies began with the Scopes Trial of 1925, a case the evolutionists actually lost.
Since 1968, however, U.S. courts have consistently held that "creationism" is a particular religious viewpoint and that teaching it in public schools would violate the First Amendment of the Constitution.
For a one page summary of important court cases, see Ten Major Court Cases about Creationism and Evolution.
Chapter 4 of Religion in the Public Schools: A Road Map for Avoiding Lawsuits and Respecting Parents' Legal Rights, by Anne Marie Lofaso, a professor of law at West Virginia University, contains a detailed review of the legal issues surrounding the teaching of evolution.