YouTube has provided a couple of great ideas for teachers. The screen shot below shows, perhaps, the most useable idea for primary teachers. It may take a little work up front, but it will pay off with engagement. You can spend time searching for applicable videos that may work the way you would like, or you can create your own, with some bravery of course, customized to your classroom needs. Despite popular belief, you can create a secure channel on YouTube that only those you choose can access. It seems that perhaps YouTube is realizing that it may need to compete with iTunes U and Vimeo. Good Luck!
Fred C. Underhill School: Principal's Blog 
I think YouTube has a wealth of resources for teaching. We can create and upload videos, and I love the use of visuals to introduce, enhance or reinforce concepts, especially for the students at our grade levels. I’m glad that our district (unlike others) has not “banned” access to YouTube, but I always, always preview an entire video clip before showing it.
Maybe we can post some of our favorite YouTube videos for teaching here?
I’ll start: I usually find YouTube video of Punxatawny Phil coming out of his burrow to show during my lesson on Groundhog Day.