California Code, Penal Code - PEN § 627.4

(a) The principal or his or her designee may refuse to register an outsider if he or she has a reasonable basis for concluding that the outsider's presence or acts would disrupt the school, its students, its teachers, or its other employees;  would result in damage to property;  or would result in the distribution or use of unlawful or controlled substances.

(b) The principal, his or her designee, or school security officer may revoke an outsider's registration if he or she has a reasonable basis for concluding that the outsider's presence on school grounds would interfere or is interfering with the peaceful conduct of the activities of the school, or would disrupt or is disrupting the school, its students, its teachers, or its other employees.