If your in need of a projection solution for your classroom, consider using a Chromecast. A Chromecast is a great solution for not only projecting the contents of your Chromebook on a screen for all to see, but if you're using a tablet such as a Nexus 9 or Nexus 7, a Chromecast may be the way to go.
Connected to a projector, the Chromecast can project everything from a Youtube video you want to show to a Google Slides presentation. And, since it's wireless, the Chromecast allows you to be on the other side of the room with your Chromebook. If you're using a tablet, it allows you mobility. You can move about the room while the contents of your tablet are displayed.
The Chromecast is easy to set up. Provided your projector has an HDMI port, simply plug the Chromecast into your projector and then into a power outlet. If your projector doesn't have an HDMI port, you'll need an adapter to plug the Chromecast into as well as the VGA cable into. Furthermore, if you go the adapter route, make sure and get an adapter with audio jack so you can plug in any speakers you wish.