In this paper, we describe a strategy called design tracing, which trains students to comprehend class and sequence diagrams by tracing different scenarios. In design tracing, for a given scenario, students identify relevant variables from the class diagram, relevant events from the sequence diagram and trace the flow of these data variables, their values and events by constructing a state diagram. We have developed a web-based learning environment - VeriSIM, which trains learners to apply design tracing to trace scenarios. We conducted a study where 88 final-year undergraduates interacted with VeriSIM. Participants took a post-test after interacting with VeriSIM. Results from the post-test show that after interacting with VeriSIM, students are able to identify relevant events, but around 50% of the students still had difficulties in identifying relevant variables and constructing the state diagram. A focus-group interview was also conducted with 13 participants in order to understand participants’ perception of the usefulness of the design tracing strategy. A thematic analysis of the focus-group interview showed that students perceived that design tracing helped them understand the relationship between different diagrams and identify different scenarios in the design. Interaction with VeriSIM also helped students understand the usefulness of creating class and sequence diagrams. These results show that design tracing can be a useful pedagogy to help learners form an integrated and correct understanding of class and sequence design diagrams.