One of the goals of the No Child Left Behind Act of 2001 (NCLB; 20 U.S.C. § 6301) was to close racial and socioeconomic achievement gaps. Over a decade has passed since NCLB went into effect. In this paper we investigate whether the Act has been successful at narrowing racial achievement gaps. Overall, our analyses provide no support for the hypothesis that No Child Left Behind has led, on average, to a narrowing of racial achievement gaps. We find that within-state achievement gaps were closing slowly, on average, prior to the passage of the NCLB legislation, and that this trend did not change significantly after the introduction of NCLB. However, we do find evidence indicating that the policy’s impact varies systematically across states in ways that are consistent with NCLB’s subgroup-specific accountability features. In states facing more subgroup-specific accountability pressure, more between-school segregation, and larger gaps prior to the implementation of the policy, NCLB appears to have narrowed white-black and white-Hispanic achievement gaps; in states facing less pressure, less segregation, and smaller pre-existing gaps, NCLB appears to have led to a widening of white-black and white-Hispanic achievement gaps. We conclude with a discussion of potential explanations for these findings.