The Classroom Performance System consists of software, a USB receiver that looks like a flying saucer, and 32 “clickers" that look like remote controls. You make up series of questions (grouped into what they call lessons) with multiple choice answers. Then you project the warm up, quiz, whatever, on your lcd projector, and the kids click the appropriate button on their clickers. You can set a time limit for each question, and it displays (live) who has answered (but not what they answered), and when the time is up, it displays how many kids chose each answer, and optionally, the correct answer. (Beauty for teaching opportunities: “Now, it looks like a lot of you chose B, and that was wrong; let’s talk about why you might have thought that was right…”)
And, even better, you can use the paper tests, quizzes, etc. that you already have. The software has a FastGrade feature which lets you simply enter the correct answers (it doesn’t need to know the questions, does it?), hand out the test, and start the software. The clickers have forward and backward buttons, and the kids can simply arrow their way though the test, answering each question by clicking the appropriate letter. They can go back and forth, and change their answers at any time. They can all be on different questions at different times and everything. If your test has short answer or essay questions too, the software lets you skip those quesions when they’re clicking, so you can grade that part after.
You can also use them to just find out if they understood what you said without embarrassing anyone. Ask a question (the software calls it a “verbal question”), click go (or whatever) and the kids click. You can see how many got it and how many didn’t without singling anyone out.
The software itself is free from eInstruction.com (right-click, and save-as). The clickers and receiver are sold separately.