The states have always been central to the American public school systems, and they have been sharply expanding their authority over local school districts since the 1980s, when they adopted education reforms that increased course requirements (especially in science and math), mandated uniform testing, and put in place higher teaching standards. A number of states also experimented with takeovers of schools and districts that were falling behind. 2002 saw the advent of the No Child Left Behind (NCLB) Act, which constituted a huge expansion of federal authority over the schools. However, NCLB relies on state education agencies to carry out its mandates to produce massive improvement in educational outcomes for all groups of students. NCLB makes the states responsible for defining student proficiency, and if schools or districts fall behind the increasingly demanding standards, as a great many have done, the law directs the states to take action to improve outcomes and grants them sweeping powers over local schools and districts. In this article, the authors explore the states' responses to NCLB and assess the likelihood that state education agencies will be able to meet the law's demands with their current knowledge and resources. (Contains 5 endnotes.)