Lots of teachers are using their iPads to airplay onto a TV with their Apple TV. This gives them the ability to have an interactive modelling book that they can prepare before a guided lesson and add to as the lesson progresses.
I was asked about which app I thought was the best for this. My short answer would be that it deepens what functions you want to use. For the simplest, cleanest interface I would use Bamboo but if you want some more features such as adding images, importing templates and documents and more then Explain Everything has it all!
Here’s a graphic I’ve made that highlights the features of three well known apps. Please share the graphic around.