We have been using Plickers, a free resource that is like clickers, but much easier to use and it uses a QR code! Students are assigned a card and they use one card to choose their answer. I use my i-pad or phone to scan the room to get immediate feedback and use that information to check formatively whether students are understanding our target for the day or if we need to go over any topics again. Everyone's code looks different and the letters are so small that no one can see what their neighbor is answering! It is such a cool resource and so easy to set up and use! It shows me automatically how the class responds and individual student responses as well.