iMovie is a wonderful tool for students and teachers to edit and create movies. It is $4.99, unless you purchase and activated your iPad after Sept. 2013, then it is free. But even at $5 totally worth it.
My favorite part of the app, besides the easy editing, is the trailers creation. Trailers are short templates that already have scenes, types of shots, transitions...created. All you have to do is drop in your media and change the text and let iMovie do its thing.
Save your movie to the camera roll or upload to YouTube (make sure to login to YouTube first).
Great resource from TCEA14 from Chris Miller from Sanger ISD