This article examines major trends in testing and accountability reform in the United States over the past decade. The review covers the apex and decline of the national experimentation with a range of alternative assessments and the rise of test-based accountability as a central policy initiative. These trends signify that testing has become a widely utilized instrument for educational reform in America. Research on these trends indicates that high stakes testing does motivate teachers and administrators to change their practices, yet the changes they motivate tend to be more superficial adjustments in content coverage and test preparation activities rather than promoting deeper improvements in instructional practice. Further, the information provided by large scale assessments is primarily useful to measure school and system progress, but of more limited utility for instructional guidance. Most problematic is that the high stakes testing system in America has been repeatedly promoted as a substantive reform in itself. However, high stakes testing is a relatively weak intervention because, while it reveals shortcomings, it does not contain the guidance and expertise to inform response. The article concludes with suggestions on how to capitalize on the strengths of high stakes testing while minimizing its shortcomings.