Pikme is a great classroom management app that can help improve student participation. Note that this app will be found under the iPhone App category. Simply enter your student names into the app, select the class name, and shake your device. The app randomly selects a student.
In addition, the app offers a quick way to group students. Tap the button, modify the group settings, and tap CREATE. The 1 1/2 minute video below shows a few additional features: