Assessing engineering students' technical knowledge is an important concern in engineering education. We suggest that one way to do this is by using concept inventories. These have been developed and standardized for an increasing number of the disciplines. As part of a larger NSF funded project focused on developing, incorporating and assessing Model Eliciting Activities (MEAs), we have turned to concept inventories (CI) in general, and a subset of the CI - knowledge tests (KT) - as a means of assessing conceptual understanding. The knowledge tests are focused on the particular concepts that are designed into the MEA. Included in the knowledge tests is a selfassessment of the student's level of confidence in answering each question. We are interested in studying the relative effect that MEAs designed around specific concepts can have on student learning compared to more traditional instructional methods. Although MEAs were originally designed to improve the understanding of technical concepts, our earlier research has found that they do improve students' problem solving and professional skills and result in significant learning gains; however, they may only marginally increase students' level of knowledge compared to more traditional methods. In this paper we provide an in-depth investigation of how measuring both students' performance as well as their confidence is affected by exposure to MEAs. Specifically, we ask the following: is there a significant gain in students' knowledge from the beginning to the end of the semester; are students who are most confident in their answers also correct in their responses; is there a gender difference; and, do differences exist between sections that used MEAs versus those that did not?