Research shows that using computer-aided mapping tools improves critical thinking skills, but prior research provides limited evidence to show how the use of specific critical thinking skills increases map quality. This qualitative study observed 4 experts and 5 novices use a computer-aided mapping tool to construct argument maps. The analysis of video recordings with think-aloud protocols and retrospective interviews revealed the use of a five-step argument mapping process (read claims, position conclusion, position claims, link claims, revise links) with the experts using a more sequential application of the five-step process and producing more accurate maps than novices. The novices showed the tendency to position and link claims as a joint action, making map revision more cumbersome. The experts exhibited the tendency to work backward from conclusion to claim while the novices exhibited the reverse tendency. This study's findings identify processes that differentiate experts from novices and validate specific thinking skills that can be used to improve map quality, and how these processes can be operationalized in terms of discrete mapping behaviors performed on screen that can be mined and analyzed in mapping tools to assess and diagnose students' mapping skills.