RESEARCH REPORT When and Why a Failed Test Potentiates the Effectiveness of Subsequent Study Matthew Jensen Hays University of Southern California Nate Kornell Williams College Robert A. Bjork University of California, Los Angeles Teachers and trainers often try to prevent learners from making errors, but recent findings (e.g., Kornell, Hays, & Bjork, 2009) have demonstrated that tests can potentiate subsequent learning even when the correct answer is difficult or impossible to generate (e.g., “What is Nate Kornell’s middle name?”). In 3 experiments, we explored when and why a failed test enhances learning. We found that failed tests followed by immediate feedback produced greater retention than did a presentation-only condition. Failed tests followed by delayed feedback, by contrast, did not produce such a benefit— except when the direction of the final test was reversed (i.e., the participants were provided with the target and had to produce the original cue). Our findings suggest that generating an incorrect response to a cue both activates the semantic network associated with the cue and suppresses the correct response. These processes appear to have 2 consequences: If feedback is presented immediately, the semantic activation enhances the mapping of the cue to the correct response; if feedback is presented at a delay, the prior suppression boosts the learning of the suppressed response. Keywords: spacing, testing, retrieval, forgetting, errorless learning Tests are perhaps the most ubiquitous element of formal edu- cation. For hundreds of years, almost every lecture, lab, and seminar has concluded with a test. These criterion tests are in- tended to diagnose the knowledge or ability possessed by the student or trainee. In the past century, however, researchers have discovered that tests do more than diagnose; they are potent learning events (e.g., Gates, 1917; Spitzer, 1939). That is, tests serve to create and/or strengthen associations between information in memory. Indeed, successfully retrieving information during learning often creates stronger memories than does re-studying (e.g., Allen, Mahler, & Estes, 1969). This testing effect has been demonstrated in a variety of domains, including children’s picture naming (Wheeler & Roediger, 1992), high-school students’ com- prehension of history lessons (Nungester & Duchastel, 1982), college students’ comprehension of cognitive psychology course material (Leeming, 2002), and undergraduate students’ recollec- tion of idea units from prose passages (Roediger & Karpicke, 2006). Nevertheless, tests are rarely used to improve learners’ compre- hension or competence in mainstream education (e.g., Glover, 1989). The threat of a test is often used to encourage students to study more (but with little effect on learning; see Haynie, 1997). Educators may be reluctant to employ tests as learning events for fear of the effects of incorrect responses. This fear is not without substance. Butler and Peterson (1965) found that errors on tests can be “stamped in,” meaning that producing an incorrect response will cause that same incorrect response to be produced on later tests (but see Metcalfe & Kornell, 2007). These findings reinforced the emerging “errorless learning” movement (e.g., Terrace, 1963), which posited that errors weakened instruction and created un- wanted by-products of the training process. Indeed, errorless learn- ing does appear to benefit clinical populations (e.g., Kern, Liber- man, Kopelowicz, Mintz, & Green, 2002; Kessels & de Haan, 2003). In normal classrooms and training settings, however, research suggests that tests should still be used— even if students some- times respond incorrectly (e.g., Marsh, Roediger, Bjork, & Bjork, 2007; Pashler, Zarow, & Triplett, 2003). Failed tests, it seems, do not overwrite previously learned information or otherwise corrupt cognition. Further, failed tests do not reduce the value of later learning. On the contrary, Kornell et al. (2009) found that presen- This article was published Online First May 14, 2012. Matthew Jensen Hays, Institute for Creative Technologies, University of Southern California; Nate Kornell, Department of Psychology, Williams College; Robert A. Bjork, Department of Psychology, University of Cali- fornia, Los Angeles. Grant 29192G from the McDonnell Foundation supported this research. We thank the members of CogFog for their suggestions and interpretations of the findings reported in this article. We especially thank Barbara Knowlton and John Nestojko for critical methodological suggestions throughout our research. Correspondence concerning this article should be addressed to Matthew Jensen Hays, USC–ICT, 12015 Waterfront Drive, Los Angeles, CA 90094. E-mail: matt@hayslab.com Journal of Experimental Psychology: © 2012 American Psychological Association Learning, Memory, and Cognition 2013, Vol. 39, No. 1, 290 –296 0278-7393/12/$12.00 DOI: 10.1037/a0028468 290