Here is a little video I made a while ago to show off the potential uses of the iPad in a math class. I used the app ShowMe but there are other apps available such as EduCreations.
So far I've used this on days when I've been absent. I created videos the substitute could play. I've thought about creating videos of our notes and having the students watch it before class, but I don't think they would....
I think the most effective time would be to post videos of how to work sample test questions the days before a big test.
What other times would this be effective?