Effective instruction in Engineering and Technology requires knowledge of how students understand or lack understanding of key concepts in these disciplines. Incorrect mental models, deeply rooted in everyday experience, can significantly affect student learning. Evidence suggests that students who learn new material may already have some understanding and preconceptions about the new concepts. Misconceptions about electricity of novice students (college freshmen and first-semester sophomores) were analyzed and compared to the misconceptions of senior students. The study targeted: (1) correlation between student academic success (grades) and student misconceptions, and (2) understanding how student mental models and misconceptions change with increasing levels of competency and expertise during students' progression from the freshman to senior level. Non-equivalent groups of 20 novices and 22 seniors participated in this study. The mixed-methods research methodology included two phases. In the quantitative phase all students responded to the Concept Inventory [1] questions. During the qualitative phase 8 novices and 8 seniors were interviewed and responded to open-ended questions about their understanding of electricity.