Educreations is one of my favourite iPad apps. It is essentially a whiteboard that allows you to draw, annotate on photos from your iPad camera or library, record audio while you are working, and pull in material from your Dropbox account. When I first came across this app, I imagined it being used by peer tutors to create mini-lessons for tutees that could be saved on an online Educreations account for access anywhere. I envision this app being used from K-12 as there are multiple uses and it really isn't grade-specific. I just read this interesting post from a kindergarten teacher by the name of Carrie Both who is using this app to assess her students' ability to retell the major events from a story. You can have a look at her application of Educreations here.