Concept maps have proven beneficial in the assessment of students' preconceptions and mental models in the natural sciences. This paper examines if it is possible to create concept-map class diagrams from the Unified Modeling Language to assess student's mental models upon entry into a course and to monitor their development throughout the course. Perhaps the use of UML in the cognitive area will facilitate students' understanding of object-oriented software design. Hopefully the mental models obtained can make instructional designers cognizant of the common misconceptions and pitfalls students have in the conceptually challenging area of object-oriented software design.