Our goal is to develop a cognitive model of how humans acquire skills on complex, sensorimotor tasks. To achieve this goai, we collected data from subjects learning the NRL Navigation task, then used the data to construct a model that reflects the bcisic, cognitive elements required to learn and thereby succeed at this task (Gordon & Subramzuiian, 1997). This paper describes a new experiment with humcin subjects on the task. Data from this experiment not only confirms the key cognitive element of our model, but also helps us better understand individual differences in learning this task. Four evaluation metrics indicate that we are able to model important trends in the evolution of action choice.