Today, the role of high-stakes assessments in educational accountability is challenging long and enduring understandings about the function and character of testing in society. In essence, test-based accountability is now seen as a powerful policy lever used to steer school improvement (Linn, this volume). Although there were precursors in the 1980s and 1990s, it was the passage of No Child Left Behind (NCLB, 2002) legislation that institutionalized a reliance on standardized test score performance or test-based accountability as a key mechanism for improving student achievement.