Last week, I downloaded the Showme Interactive Whiteboard app onto my iPad. In just a few minutes, I learned how to create a presentation for students that showed them how to order decimals. My struggling math students watched the presentation once. Then they watched it a second time, pausing it before the presentation gave them the correct answer to see if they remembered how to fill in zeros for decimal places and accurately order decimals with different place values. I had these same students create their own showme to explain the process with a different set of decimals.
I have watched more complex presentations on youtube (http://www.youtube.com/watch?v=40Hk2PA8Diw&feature=related) where it shows how students can download a picture in order to narrate a presentation. What a great app for helping students not only understand and review concepts, but also practice explaining and verbalizing sequences and procedures!