A Materials Concept Inventory (MCI) has been created to measure conceptual knowledge gain in introductory materials engineering courses. The 30-question, multiple-choice MCI test has been administered as a pre and post-test at Arizona State University (ASU) and Texas A & M University (TAMU) to classes ranging in size from 16 to 90 students. The results on the pre-test (entering class) showed both "prior misconceptions" and knowledge gaps that resulted from earlier coursework in chemistry and, to a lesser extent, in geometry. The post-test (exiting class) showed both that some "prior misconceptions" persisted and also that new "spontaneous misconceptions" had been created during the course of the class. Most classes showed a limited, 15% to 20%, gain in knowledge between pre and post-test scores, but one class, which used active learning, showed a gain of 38%. More details on these results, on differences in results between ASU and TAMU, and on the nature of students' conceptual knowledge will be described.