"Depending on the severity, I would probably stop the bus. I don't feel comfortable operating a large vehicle while there could be violence happening in my rear view mirror. I would rather resolve the issue before it escalates. Usually I need to separate the kids, but if I needed to I would discipline them as well."

Give an example that shows you can deal with these types of situations. Your ability to handle conflict between students will greatly improve the quality of life on your bus route and make you an even better driver!