This chapter discusses the federal government's role in strengthening accountability for student performance under the No Child Left Behind Act of 2001 (NCLB). NCLB represents a major legislative expansion of the role of the federal government in elementary and secondary education, and it has had significant implications for federal-state relationships. A special focus of the new law was the "adequate yearly progress" (AYP) measure, which had been included in the 1994 law as an aggregate measure of school progress in meeting state proficiency goals. Under the 2001 law, AYP had to be disaggregated for major subgroups, and there were more specific consequences when districts and schools did not meet AYP. Highlights of these key new requirements included the following: (1) A 100% proficient deadline was set for all students, and disaggregated data were used to determine AYP toward that deadline; (2) Graduation and participation rates were included to ensure high levels of student participation in testing; (3) Test requirements were added; more grades were tested in language arts and mathematics and a science assessment was added; (4) States are required to participate in the NAEP; (5) Actions are required when Title I schools do not meet state AYP; (6) Strategies used must be grounded in scientifically based research; and (7) Teachers are required to meet a federal definition of highly qualified. Additional funds were appropriated for states, schools, and districts to help implement the law. Table 1 shows the accountability requirements that the 1994 law put in place and additional requirements under NCLB that apply to states, districts, and schools. [This article represents Chapter 7 of "The Elementary and Secondary Education Act at 40: Reviews of Research, Policy Implementation, Critical Perspectives, and Reflections," "Review of Research in Education," v29, 2005 (EJ748131).]