Our science classes tried out an app called Plickers. Students held up papers with random shape that are similar to a QR code, and rotated the papers to show their answers. The app used the camera on my iPad to scan which code was held in what rotation. This was recorded, and I received instant feedback. In this instance, we used Plickers in our unit review. It required a little getting used to, but the students said that it made for a fun review.