In this article, the authors describe various rationales for accountability testing programs over the past century. This history forms the backdrop for current test-driven reforms, including Public Law 107-110, the No Child Left Behind Act of 2001 (NCLB), which was signed into law in January 2002. The goals of the authors are first, to illustrate the diversity of mechanisms whereby testing may affect educational practice and learning outcomes, and second, to show that while many of the same ideas have recurred over time in different forms and guises, accountability testing "has" become more sophisticated. There is a better understanding today than in the past of how to make accountability testing an effective policy tool, although it remains to be seen if one will make the best use of this understanding. Testing may subtly shift the blame for school failure from inadequate school resources, poor teacher preparation, or out-of-school factors to teachers and students who are "simply not working hard enough," and thereby divert attention from more costly, more needed reforms. The authors describe testing during different periods, from the early 20th century to the present. Most of these periods are characterized by one or another predominant mode of test use in education. Where appropriate, the authors refer back to the earlier roots of testing applications characteristic of a given period. (Contains 2 figures and 2 notes.)