All school staff and employees, including bus drivers and other staff, are under the same restrictions as teachers with respect to religious interaction with students. Bus drivers and other staff are also agents of the state and, therefore, capable of violating the Establishment Clause.
However, just as with teachers, when bus drivers or other school personnel are away from the school and on their own time, they may interact with students about religion.
Several other situations may arise with bus drivers. For instance, a bus driver is generally not permitted to play religious music on the bus or to have a Bible visible on the bus while students are on board. However, a bus driver could permit students to take turns choosing a radio station and religious students could be permitted to choose a religious station when their turn came. Also, bus drivers should permit students to interact privately with each other regarding religion while on the bus, as long as the interaction does not constitute harassment.
—Keeping Christ in America’s Public Schools, Gibbs & Gibbs, 2008