Show one screen, hide another? I'm a teacher, and I like to cast my laptop screen to the television in my classroom via Apple TV.  However, there are times I'd like my students to see one screen while I work on a different one they cannot see.  

I don't have multiple monitors.  I know there is a way to do this but can't figure it out!
The following solution assumes that you are using a Mac running OS X Mavericks, and is connected to the same Wi-Fi network as your Apple TV.

You can use the Apple TV as a secondary display over AirPlay. Go to System Preferences → Displays, and select your Apple TV under AirPlay Display.



You can both mirror the contents of your Mac, or use Apple TV as a second display (your desired use case).

Go to Arrangements under Display preferences and uncheck Mirror Displays to use Apple TV as an extended display.