The purpose of this study was to investigate the influence of game-like activities on adult learning during a computer-based simulation. This research also studied the use of visual metaphors as graphic organizers to help make the underlying science principles explicit without interfering with the interactive nature of the simulation. A total of 70 university students participated in the quantitative phase of the study. They interacted with a simple computer simulation that modeled the relationship between acceleration and velocity using a discovery-based approach. No formal instruction on the science concepts was given. Participants had control over the acceleration of a computer-animated ball. In the quantitative phase of the study, four simulation conditions were studied comprising two levels of two factors: Gaming Context (Yes, No) and Visual Metaphor (Yes, No). Results from the quantitative phase showed that although participants reported greater levels of enjoyment when the game was included, the game actually interfered with participants' explicit learning of the science principles. No effect for the visual metaphor was found. However, the use of the game in tandem with the metaphor resulted in increased levels of tacit learning, as evidenced by greater scores on a special gaming task used for evaluation at the end of the session. In the qualitative phase, four additional participants were interviewed as they interacted with a version of the software which allowed each of the conditions to be switched on and off. Qualitative results demonstrated that the visual metaphor became a very important tool for participants. Also, the qualitative sessions uncovered patterns of interaction while playing the game that might explain why the game interfered with learning. These results are important given the recent increase in interest in gaming among educators. (Contains 3 figures and 1 note.) [Abstract also provided in French, German and Spanish.]