Since some of the response systems cost money for use on 30 iPad2, I have chosen to incorporate Polleverywhere as an informal assessment tool. I like the fact that since I created a classroom site specific to Polleverywhere we can easily access the web version for responses.
I know Polleverywhere is not a new tool, as I actually used it at the beginning of 2009 it is a tool that I have pulled back out from the tech toolbox and used quite successfully. To set up your own Polleverywhere site see their directions.
Below is actual footage of the process from actual participants in my math class.