We present an evaluation of a multimedia educational software system that includes text, graphics, animations, and simulations. When compared with an informationally equivalent control environment that used text and carefully selected still images, we found little evidence that the dynamic presentations enhanced student understanding of the declarative information in this lesson. Furthermore, students cannot be relied on to take full advantage of exploratory opportunities in computer-based instruction. These results prescribe further investigation of whether and how computer-based multimedia can be used effectively in education and training.