What should the bus driver do after ensuring no traffic is coming when pupils are loading?

A bus driver has the responsibility to ensure the safety of children as they board or disembark from the bus. After confirming that there is no oncoming traffic, the appropriate action is to use a clear and visible signal for the students. Waving an arm to indicate that it is safe to cross is an effective way to communicate with the pupils, indicating that they can proceed safely. This action not only provides a clear visual cue, but also helps to increase the driver's visibility and presence, ensuring that students feel confident and secure as they move towards the bus.

The other choices presented may not effectively reinforce safety. Calling out to the students does provide auditory communication, but it lacks the clear visual signal that waving an arm entails. Opening the door quickly may potentially rush students or create a sense of urgency, which could lead to accidents. Checking mirrors again, while always a good practice, would not be necessary if the driver has already ensured that no traffic is present. Thus, signaling through an arm wave is the most appropriate and effective action to ensure safe loading for the students.