This site discusses the app Explain Everything, which I used to make my first digital storytelling presentation. It is great for a little bit of screen casting on a tablet. The app lets you export as a video as well.
This site offers a wealth of information and many great resources for teachers interested in using digital media for storytelling and other activities. There are a number of very good, clear, screencast tutorials for teachers to use. Preview a few to see if you might be able to use them with your classes. I thought they were great for high school students, and they inspired me to think about creating my own screencasts for other tutorials! :-)