how does one really achieve great classroom management skills?

Today while observing, I noticed that the biggest struggle in most classrooms is managing student behavior.  I'm a product of Catholic school, so students misbehaving to the degree I've been witnessing weren’t even a thought in my fellow high school peers minds.  Now, that’s not to say that my high school didn’t have its fair share of kids who would act out, but it was nothing compared to what I've been observing.  In one of the classes I observed today, made up of 3 female students and 21 male students, the level of noise was so great that I couldn’t hear my self think, let alone the teacher verbally give out n assignment.  The teacher was giving the students a journal prompt to write about; she had to repeat the question 4 times, and still students were asking what the question was.  I began to get really frustrated!  This teacher is a veteran teacher, and to be honest I expected her to be able to control her students better than any other teacher, but that wasn’t the case at all.  I'm unsure of why the classroom got so out of control in the first place.  What was causing these students to have such a lack of respect for their teacher?  What was giving the teacher such patience that she didn’t run out of the room and never return?  It made me start thinking about my own future classroom.  What if my future students behave that way?  Do I have a plan of action to deal with a situation like that?  Or better yet, what can I do to prevent a situation like that from happening?  The teacher I observed put on a movie for the rest of the period, and that seemed to settle the students to a certain extent, and could almost swear I saw her raise a little white flag from behind her desk!  Ok, so maybe she didn’t actually raise a little white flag, but she may as well have.  The people I really felt bad for were the students who were actually trying to learn.  I can’t imagine how annoying and distracting it must be to be in a classroom where the majority of the period is based around the teacher telling your peers to pipe down and pay attention.