However, when I was a student I found some of the class would get distracted and the teacher would raise their voice to get the students back into focus. I have also seen classes of school children on the street and the teacher raising her voice at them because she is worried about their safety.
Of course we both know there are correct and incorrect ways of speaking to people and sometimes teachers do lack tact but this could be put down to frustration. It is difficult to control a large group at the best of times and especially if they happen to be young children.
These kids should count themselves lucky that CP is no longer in force when they manage to wander off the track.