In an earlier study, Strober and Cook (1992) used videotapes to examine the types of errors that novice economics students made in graphic analysis of a simple supply-demand problem. In this article, we extend that work by replicating the earlier findings, improving the framework for analyzing errors, and examining some methods used by novice groups to correct errors. We describe the categories of cognitive errors and error-correction techniques that we developed from the cognitive psychology literature and watching the tapes. We then provide discussions by group, to give a sense of the context in which the errors were made and corrected. The categories used for the analysis were cognitive and social rather than conceptual. These categories should prove useful for extending our understanding of why and how students make errors to other types of economics problems.' In the last several years, the field of cognitive psychology has witnessed several exciting breakthroughs concerning student learning (Bruer 1994). A cardinal tenet of the new cognitive psychology is that the errors made by students are not random but have patterns that a careful observer can detect. Our work was in the spirit of this new cognitive psychology; we used the videotapes to find and to learn from patterns in student errors. Cognitive psychologists argue that unless the errors students make are specifically corrected, learning is inhibited (Bransford and Vye 1989; Anderson 1989).