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…

Taking tests enhances learning. But what happens when one cannot answer a test question--does an unsuccessful retrieval attempt impede future learning or enhance it? The authors examined this question using materials that ensured that retrieval attempts would be unsuccessful. In Experiments 1 and 2, participants were asked fictional…