Personal Response Systems or clickers have been used for a number of years to help create active learning environments in the lecture classroom.  Researchers have shown that the use of clickers stimulate student-student and student-lecturer interaction.  In addition, students value the use of clickers and feel that these devices contribute to their understanding.  Even though clickers have been used for quite some time, there are relatively few research studies focusing on how student knowledge is enhanced through the use of clickers.  To contribute to this body of research, we compared student responses on exam questions to similar or identical clicker questions that were presented during lecture.  The analysis of the responses to both clicker and exam questions show how individual student knowledge evolves during instruction.  Although there is evidence of improvement during lecture, many students were unable to respond correctly when the questions were posed on the exam, despite the similarity in the questions.