Electronic response systems, familiar to many television viewers as the technology used to poll the audience on the game show "Who Wants To Be a Millionaire," are the newest classroom technology for determining whether students understand material that has been presented. Students answer questions with individual keypads ("clickers"), a base unit receives the IR or radio-frequency signal, and a software program tabulates the responses and displays them as a histogram. The latest generation of clickers allows students to enter numeric or text answers (up to about 30 characters). When used in a pedagogically sound manner, response systems give instant feedback and allow teachers to provide timely help when students have difficulty mastering concepts. In addition, the results of each class session are compiled in a database, simplifying the task of taking attendance or giving quizzes in large classes. Students are generally very positive about the systems except when they are used solely for electronic roll-taking or when the teacher ignores student misunderstandings.