In Search Of Answers, Teachers Turn To Clickers : NPR
http://www.npr.org/templates/story/story.php?storyId=101343866

Text and audio versions of story

All Things Considered, March 2, 2009 · Teachers know the blank stare. It can be hard to know what students are absorbing in class. Well, technology to the rescue. More teachers are equipping their classrooms with little keypads — often called clickers — that let students instantly, and anonymously, answer questions. Teachers say the clickers are improving the quality of education by measuring how engaged students are in the material they are learning.

In Search Of Answers, Teachers Turn To Clickers - all things considered