Socrative

This application allows your students to take quizzes through a mobile device or computer while in a virtual classroom. The quizzes can be taken while in an actual classroom setting, or can be designed to work as an at home quiz. It offers multiple choice or short answer, and you can decide to put in a correct answer and/or explanation.
I have used this before on the student side in my German class. My teacher uses it as a short answer quiz, and displays the answers on the projector as we take the quiz. She has made it into an interactive exercise rather than a personal quiz. I like that it is so adaptable to whatever you want to do in or outside of the classroom. I designed mine with a variety of questions that tested knowledge and opinion, and worked with a sample group of students that ranged from ages 11 to 39. My German instructor uses the teacher based quiz for her classroom activities, but if this was assigned as an at home quiz, I would use the student paced.
My concern would be that they would get off task with an electronic device in front of them while in class. While it works for my German teacher in a college setting, it would be a different world trying to get middle or high school students to stay on task. If the teacher commands enough respect though (not the tyrant type, but the loved and respected type), they may be able to motivate students to do well because this type of quizzing uses cool technology.
Overall I am excited to test this application out in my classroom. It may not be the best for strict mathematical questions, but using it for one question a day they need to complete as an "exit ticket" would be a fun way to engage them in what we were learning that day.