UPDATE: Google TV with Chromecast now supports codes for a more secure casting environment in your classroom! Much like the security codes in AppleTV, Google TV with Chromecast now supports Cast Moderator. How does this work in a classroom? If you or a student wish to cast, you'll select "cast" and then you'll be asked to enter the code that shows on the screen. This now prevents kids who are casting on their Chromebooks from begin able to kick one another or you, the teacher, off of the screen. The video below shows how to set it up.
I use my Chromecasts constantly! In fact, I'm using one today for this presentation! I love the way that it plays videos smoothly by eliminating the middleman. I love using my phone to teach with. At home, it's my favorite way to watch TV! We now have them in EVERY classroom at school! Chromecast is the preferred method (even over AppleTV) to cast screens and especially to play media on our classroom TV's. They're inexpensive and they just work. They also work seamlessly with Chromebooks!
Get the Chromecast with Google TV HERE