https://plickers.com/) in their classrooms for quick formative assessments and checks for understanding during instruction. Plickers provides realtime formative assessment data and only the teacher needs to have a device - not the students.
Teachers need to setup an account and load the app, either IOS or Android, on their tablet or smartphone; and both are free. There are also pre-made Plickers card sets you can download for students to use.
It's also a great tool to use to survey staff during meetings and professional development.
IOS app: https://itunes.apple.com/us/app/plickers/id701184049?mt=8
Android app: https://play.google.com/store/apps/details?id=com.plickers.client.android
Here are some ideas and resources for using Plickers in your classroom: