behavior in a classroom

So I got to witness some of the hard things today in my observation class. When we talk in our class about spending only a small portion of time on teaching but most on discipline, I agreed with it but never actually believed it. Today, I changed my view. We had the "trouble makers" in my class today because the class was divided and half went next door and half of the kids next door came into our room. Well, the class was extremely disruptive and got nothing done. My co-op teacher spent more time yelling at them to sit, or to be quiet instead of shouting, or to keep their hands to themselves. We could barely have a conversation without someone telling on someone else or getting in trouble. I've never seen my teacher so upset. There was one student who threw his chair and so she told him to come and sit on the other side of the room. He said no, and started to pout. She told probably at least 3 or 4 times and he refused. Ive never seen a student disrespect a teacher so much. She eventually said fine, stay there but sit down. He pouted some more and eventually sat. That took at least 5 minutes though. And it is so dispruptive. There were a few students who were actually trying to do their work but they couldnt becaus they were dealing with this int he background. It is so shocking how much time one kid can take when there is a class of 20 other students just waiting. Discipline is a hard thing to do. When do u just deal with it and when do you try to straighten things out? Is it fair to the other students who have to deal with it? There is that fine line there where you want to keep order in the room but u want to keep the class moving as well. I truely believe that discipline takes more time than teaching actually does.