Many policymakers feel pressure to claim that No Child Left Behind (NCLB) is boosting student performance, as Congress reconsiders the federal government's role in school reform. But how should politicians and activists gauge NCLB's effects? The authors offer evidence on three barometers of student performance, drawing from the National Assessment of Educational Progress (NAEP) and state data spanning the 1992-2006 period. Focusing on the performance of fourth graders, where gains have been strongest since the early 1970s, the authors find that earlier test score growth has largely faded since enactment of NCLB in 2002. Gains in math achievement have persisted in the post-NCLB period, albeit at a slower rate of growth. Performance in many states continues to apparently climb. But the bar defining proficiency is set much lower in most states, compared with the NAEP definition, and the disparity between state and federal results has grown since 2001. Progress seen in the 1990s in narrowing achievement gaps has largely disappeared in the post-NCLB era. (Contains 3 figures, 2 tables and 6 notes.)