Testing students on information that they do not know might seem like a fruitless endeavor. After all, why give anyone a test that they are guaranteed to fail because they have not yet learned the material? Remarkably, a growing body of research indicates that such testing--formally known as "prequestioning" or "pretesting"--can benefit learning if there is an opportunity to study the correct answers afterwards. This "prequestioning effect" or "pretesting effect" has been successfully demonstrated with a variety of learning materials, despite many erroneous responses being generated on initial tests, and in conjunction with text materials, videos, lectures, and/or correct answer feedback. In this review, we summarize the emerging evidence for prequestioning and pretesting effects on memory and transfer of learning. Uses of pre-instruction testing in the classroom, theoretical explanations, and other considerations are addressed. The evidence to date indicates that prequestioning and pretesting can often enhance learning, but the extent of that enhancement may vary due to differences in procedure or how learning is assessed. The underlying cognitive mechanisms, which can be represented by a three-stage framework, appear to involve test-induced changes in subsequent learning behaviors and possibly other processes. Further research is needed to clarify moderating factors, theoretical issues, and best practices for educational applications.