When in a school zone, when must a driver stop?

In a school zone, a driver must stop when directed by a signal or a crossing guard. This is essential for ensuring the safety of children who may be crossing the street to get to or from school. The presence of a crossing guard indicates that there are children in the area, and the guard's instructions are designed to protect these children by managing traffic effectively.

While the other options may seem relevant, they do not capture the specific requirement for stopping in all instances. For instance, stopping only when school is in session neglects the times when children might be present, such as during after-school activities or events. Stopping when children are in the vicinity is also critical; however, this does not encapsulate the requirement to follow the direction of a crossing guard or signal, which takes priority for pedestrian safety. Thus, the focus on following a crossing guard's directives is vital for maintaining order and protecting young pedestrians.