One of the most hotly debated K-12 education issues in recent decades has been the appropriate federal role in defining how states should measure, identify, and intervene in low-performing schools. In December 2015, after more than a decade of complex debate, Congress passed the Every Student Succeeds Act (ESSA) to reauthorize the Elementary and Secondary Education Act of 1965, thus replacing No Child Left Behind (NCLB). ESSA enabled states to consider new ways to hold schools accountable for student achievement and other metrics and provided substantial flexibility in deciding how to improve low-performing schools. But ESSA's passage did not change school accountability overnight. It took time for the Department of Education to provide guidance on ESSA's implementation and for states to develop new systems and policies to implement ESSA's requirements. While ESSA passed five years ago, researchers and policymakers are just now beginning to evaluate the ways states have leveraged its flexibility to design and implement new accountability systems. As a senior policy adviser to Senator Lamar Alexander (R-TN), chairman of the US Senate Health, Education, Labor, and Pensions Committee, the author of this report served as the principal drafter and negotiator for ESSA. In this report, the author gives a broad overview of ESSA's new requirements for state accountability systems and describes how two states, Louisiana and Tennessee, have leveraged the flexibility of these requirements to design distinct accountability systems.