As government employees, teachers are free to practice their faith at appropriate times while on the job. Because of Establishment Clause concerns, however, teachers may not exercise this right with or in the presence of students. Teachers who wish to pray or engage in other group religious activities must do so outside the presence of students.
Teachers have free speech rights to conduct their won prayer and Bible study with their fellow teachers and/or parents. Such free speech rights may be exercised only when no students are present. Teachers and school staff must be permitted to form prayer and Bible study groups among themselves and use the faculty room for such a meeting if other groups are permitted to organize and use the faculty room (or other location) for nonreligious, nonwork-related gatherings. In fact, the school would be interfering with the free speech rights of the teachers if it prohibited them from meeting together for this purpose merely because their activity was religious. The United States Supreme Court has held that prayer and other types of religious activity are a form of free speech protected by the Constitution. meeting, they must be careful to let other employees know that their participation or lack of it
Teachers should be careful not to draw the attention of students to such religiously oriented meetings. Finally, if a teacher (or other supervisory personnel) participates in the in the religious meetings, will not affect their job with respect to hiring, promotion, or termination.
—Keeping Christ in America’s Public Schools, Gibbs & Gibbs, 2008