Student evaluations of a large General Psychology course indicate that students enjoy the class a great deal, yet attendance is low. An experiment was conducted to evaluate a personal response system as a solution. Attendance rose by 30% as compared to extra credit as an inducement, but was equivalent to offering pop quizzes. Performance on test items targeted by in-class questions rose by an average of 21% while control test questions rose by only 3%. The effect is seen in both factual and conceptual test items. Two theories that may explain the effect are discussed. (Contains 2 figures and 3 footnotes.)