Models of skill acquisition suggest that learners go through three phrases: (1) cognitive phase--when instruction is most effective, errors are frequent, and performance is inconsistent; (2) associative phase--when the learner begins to integrate the parts of the process or domain as a whole, and errors gradually become eliminated; and (3) autonomous phase--when the process becomes more automatic and less moderated by cognition, and there is less interference from outside distracters. In this paper, we will examine the use of the CRESST Human Performance Knowledge Mapping tool (HPKMT) as a tool for microgenetic analysis to characterize learners in the cognitive phase using Marine Corps 2^nd Lieutenants going through entry-level marksmanship training. The capability to characterize learners may direct the level of instruction or practice she is given. HPKMT is designed to measure a learner's knowledge of a domain. Learners express their understanding of a domain by graphically depicting the relations among concepts. Further, the microgenetic analysis methodology provides a finer picture of the learning process by using repeated observations throughout the period of change giving detailed analysis of how and when change occurs. By measuring a Marine's knowledge of marksmanship during classroom training, dry-fire practice, live-fire practice, and after qualification, we will have observations of their performance on the HPKMT at key stages of their learning. Our results suggest that the HPKMT has the potential to identify four types of learners in the cognitive phase: growing, declining, stable, and erratic.