Teachers should take effective measures to manage classroom discipline, such as establishing clear rules and regulations, and timely correcting students' disciplinary violations.
The class was quiet as it entered the room; Professor Umbridge was, as yet, an unknown quantity and nobody knew how strict a disciplinarian she was likely to be.
Now, of course, one of the problems you have is if you don't have discipline in the classroom, then not much knowledge is able to be given to the children because there's so much noise.