The use of a Classroom Response System (CRS) was evaluated in two sections, A and B, of a large lecture microbiology course. In Section B the instructor used the CRS technology at the beginning of the class period posing a question on content from the previous class. Students could earn extra credit if they answered the question correctly. In Section A, the class also began with an extra credit CRS question. However, CRS questions were integrated into the lecture during the entire class period. We compared the two classes to see if augmenting lectures with this technology increased student learning, confidence, attendance, and the instructor's ability to respond to student's misconceptions, over simply using the CRS as a quizzing tool. Student performance was compared using shared examination questions. The questions were categorized by how the content had been presented in class. All questions came from instructors' common lecture content, some without CRS use, and some questions where Instructor A used both lecture and CRS questions. Although Section A students scored significantly better on both types of examination questions, there was no demonstrable difference in learning based on CRS question participation. However, student survey data showed that students in Section A expressed higher confidence levels in their learning and knowledge and indicated that they interacted more with other students than did the students in Section B. In addition, Instructor A recorded more modifications to lecture content and recorded more student interaction in the course than did Instructor B.Because of increasing enrollments and tighter budgets, colleges are offering larger classes as a way to save money (5, 12). Consequently, faculty-student ratios in many introductory courses range from 1:100 to 1:500. While studies show mixed results in determining what effect class size has on student performance, a trend does emerge-new students or students with lower achievement levels have trouble in larger classes (3, 9).The current theory of learning, constructivism, is one where learning is an interpretive, recursive, building process whereby learners actively participate in the learning process in order to make meaning of new information and constructs so as to internalize this understanding as part of their own knowledge base (10). Therefore, attention to the limits of large class sizes is essential in order to maximize student achievement. Large classes inhibit types of instructional methods, strategies, and activities that are consistent with constructivism in four ways. First, learners need to make meaning of the new information in order to assimilate it into their existing knowledge base (19). Without meaning, information is often forgotten after a short period of time. As a result, learners need to interact with this new information in some way. Large classes limit this interaction, and the brief time allotted for instruction constrains the types of instructional strategies and activities that can be used to allow students ...