This paper studies how subjects in a three-person sequential step-level public good game learn to punish free riders more over time. Our current work makes several additions to the literature on other regarding behavior. First, our experiment provides evidence that subjects care about the actions that lead to an outcome as well as the outcome itself, replicating the results of A. Falk, E. Fehr and U. Fischbacher (Economic Inquiry, in press), J. Brandts and C. Sola (Games and Economic Behavior, 36(2), 138-157, 2001.) and J.H. Kagel and K. Wolfe (Working paper, Ohio State University, 1999). Second, our experiment provides one of the first tests of the newer theories of reciprocity by A. Falk and U. Fischbacher (Working paper, University of Zurich, 2000) and G. Charness and M. Rabin (Quarterly Journal of Economics, in press) that take a psychological games approach. We find that these theories fail to explain the experimental data. Finally, we examine the mechanism by which subjects learn to punish free-riding more ofter over time.