Tip for management while showing a movie: Always have something for your students to do.
Here's something fun I do to ensure students are paying attention, not goofing off, and are engaged in learning during a movie...
I call it:
It looks something like this:My students LOVE it! I've only done it twice this year. (I don't think you should over-use it.) The first time was for social studies when we watched a little movie on the Aztecs. We did it again a couple weeks ago when we watched part of a movie about the Mayflower. You can see by the words they've chosen to write down that they really paid attention, looking for the important information about the subject.
P.S. Sometimes, when I show a movie, I just have my students write down 10 interesting facts. Click HERE for a download.