Under a federal law known as the Equal Access Act, if a public high school allows any other non-curriculum related student groups to meet during non-instructional time, it must also allow student religious groups to meet on the same basis. In 2001, the U.S. Supreme Court ruled that it was lawful for elementary school students to meet on school grounds after school for religious meetings conducted by a private religious group, helping Child Evangelism Fellowship to grow almost ten-fold since then.
Christian student groups must be given the same opportunities to advertise their meetings as other groups. In the leading case, the U.S. Supreme Court ruled in 1990 that access rights for student religious groups included the right to advertise in the school newspaper, on the school bulletin board, in the annual club fair, and even on the school's public address system. A recent case suggests that even public school teachers are entitled to actively participate in after-school student religious meetings even if they take place at the same building where they teach.
Specifically, students in informal settings, such as cafeterias and hallways, may pray and discuss their religious views with each other, subject to the same rules of order that apply to other student activities and speech. Students may also speak to and attempt to persuade their peers about religious topics just as they do with regard to political issues. School officials, however, should intercede to stop student speech that constitutes harassment aimed at a particular student or a group of students.
The law is on our side on this one. There are plenty of ways that we as pastors can get involved in Public School Ministries, a great and fun form of evangelism.
A great resource for how to start a Public Campus Ministry is Living It High School Outreach.