A school crossing guard who meets the qualifications in subsection (b) of this section may stop or otherwise direct vehicles and pedestrians on a highway or on school grounds to assist: Pedestrians in the safe crossing of highways at a school crossing; School vehicles in entering and leaving school grounds; and Except in Baltimore City, vehicles that are not school vehicles in entering and leaving school grounds. A school crossing guard is qualified to direct traffic as described in subsection (a) of this section if the school crossing guard: Is 18 years of age or older; Is under the control of a local law enforcement agency or a county school board; Has completed training to perform any traffic direction duties to which the guard is assigned as prescribed by the law enforcement agency or county school board that has control over the school crossing guard; and Is wearing an appropriate uniform as specified by the law enforcement agency or county school board that has control over the school crossing guard. A person may not willfully disobey a lawful direction of a school crossing guard exercising the authority granted in this section. Nothing in this section prohibits a school crossing guard who does not meet the qualifications specified in subsection (b) of this section from assisting a pedestrian to cross a highway, providing the school crossing guard does not attempt to do so by directing traffic.