Excellent for formative assessments and reviews. All you need is one iPad or iPhone. Immediate feedback.
Community Review for Plickers
My Take
A great free tool. While set up may take a little effort, class creation was very easy with a quick export from our SMS. You can copy and paste questions & answers in from a website, .pdf, .doc, etc. Didn't take me more than a half an hour on average to populate a teacher's classes, create a dozen or so questions, and assign them. Card printing was simple. Make sure to look for the app under "iPhone" in the app store, but it works fine on an iPad. It would be nice to be able to aggregate scores, though. Right now, the reports are available per question.
How I Use It
I have trained teachers across our district on Plickers and worked with a wide range of middle school classes and subjects. Great for doing formative assessments and reviews. Gauge what the kids know (or don't) and start a great classroom discussion.