The seminal 1983 A Nation at Risk report, which warned of a “rising tide of mediocrity” in U.S. K-12 education, was among the primary stimulators of the standards-based accountability movement in the United States. Several waves of standards-based accountability followed this report throughout the 1990s. However, standards-based reform and accountability, a subset of systemic school reform, was not formalized at the federal level until the implementation of the No Child Left Behind Act (NCLB) in 2002. Standards-based accountability policies moved the federal policy focus away from educational inputs to the outcomes produced. These policies have proven long-lasting, enduring in many states for more than two decades with no end in sight. This entry provides an overview of standards-based accountability and reviews the progression and effects ...