Our objective has been to determine whether woii^ing with reductionistic models reduces students' mis- conceptions, and increases the coherence and flexibility of their expertise as they solve problems and generate expla- nations. W e conducted experimental trials of an interac- tive learning environment that provides models of circuit behavior. In these trials, w e examined students' perfor- mance on a variety of circuit problems before and after they worked with either (a) a "transport" model alone, or (b) the transport model augmented with explanations of its processes in terms of a "particle" model. T h e posttest re- sults reveal that, while both groups performed well o n a wide range of tasks, students w h o received the particle- model explanations achieved higher levels of performance on tasks that require an understanding of voltage and its distribution. W e conjecture that this is due to the particle model providing students with a mechanistic model for charge distribution that is consistent with the behavior of the transport model and that inhibits the construction and use of certain common misconceptions.