What must a driver do before leaving the driver's compartment while students are aboard?

Before leaving the driver's compartment while students are aboard, a driver must ensure that the parking brake is set. This is critical for safety, as it prevents the bus from rolling away while unattended. Ensuring that the parking brake is engaged secures the vehicle and protects the students who are on board, maintaining a safe environment.

While other actions like restarting the engine and placing the transmission in park are relevant to the operation of a vehicle, they are not specifically necessary before leaving the driver’s seat with passengers aboard. Setting the parking brake stands out as a fundamental safety procedure that must be performed to protect the safety of all students on the bus.