Minersville School District v. Gobitis (1940)
In 1935 two Jehovah's Witness students, 12-year-old Lillian Gobitis and her 10-year-old brother William were expelled from school for refusing to salute the flag in their Minersville, Pennsylvania school.  Saluting the flag violated their religious beliefs because it was a form of "idolatry" or worship of "graven images."

After both the federal district and appeals court decided in the students' favor, the US Supreme Court in its 1940 decision in Minersville School District v. Gobitis ruled 8-1 in favor of the school.   The Court held that instilling patriotism was a legitimate goal and that schools should train students in "a common feeling for a common country."  It was not the role of the Court to interfere with educational policy or to be "the school board for the country."

http://www.oyez.org/cases/1901-1939/1939/1939_690/