Inko is a collaborative whiteboard for iPhone, iPad, and AppleTV.
If all of your students have access to iOS devices, then Inko may be something to check out. Once installed, teachers and students can collaborate on the same whiteboard, while also displaying the whiteboard on a large screen through the use of an Apple TV app.
Unfortunately, the pricing could be a hindrance. The free version can only be used for 5 minutes of collaboration. This is pretty limited, and it costs $20 to get past. Unfortunately, everyone who is collaborating has to pay the $20. There is one more option, a designated Hero, paying ($12 a month or $100 a year) can share a white board for unlimited time with free users.