AbstractSince No Child Left Behind was signed into law, test-based accountability has become a core feature of the K-12 public education system in the United States. The approach, it would seem, is here to stay. Yet that is not to say that anything resembling a consensus has emerged. Over the past twenty years, critics have continued to raise questions about the theory of change underlying test-based accountability, and scholars have detailed a variety of unintended consequences associated with it.If test-based accountability is both likely to persist and imperfect in its design, then it is critical to consider how its shortcomings might be addressed. In service of that aim, and in keeping with the mission of this feature, this Policy Dialogue explores future possibilities by starting, first, with a look at the past. In this particular case, participants were asked to address one simple question: “What have we learned from two decades of high-stakes testing?”As regular readers of HEQ are aware, these dialogues usually feature a historian in conversation with a scholar or practitioner from the world of policy. In this case, the choice of Diane Ravitch was a natural one, particularly given the fact that she is a member of HEQ's editorial board. A research professor at New York University, she is also a former assistant US secretary of education and the author of several books about measurement and accountability.Rather than select a single interlocutor, however, the editors chose to pair her with three leaders who represent the broad range of viewpoints in the field: Denise Forte, Princess Moss, and Paul Reville. Denise Forte is the interim CEO of The Education Trust. She brings to our conversation twenty years of experience in congressional staff roles, including as the staff director for the House Committee on Education and the Workforce. Princess Moss is vice president of the National Education Association and cochair of the NEA's task force on measurement and accountability. In prior work with the NEA's Executive Committee, she helped develop the group's position on reauthorization of the Elementary and Secondary Education Act—from NCLB to the Every Student Succeeds Act. Paul Reville is the Francis Keppel Professor of Practice of Educational Policy and Administration at the Harvard Graduate School of Education and former secretary of education for the Commonwealth of Massachusetts. Nearly a decade before the passage of NCLB, he played a key role in the development of the Massachusetts Education Reform Act of 1993, which instituted standards-based accountability across the state.HEQ Policy Dialogues are, by design, intended to promote an informal, free exchange of ideas between scholars. At the end of the exchange, we offer a list of references for readers who wish to follow up on sources relevant to the discussion.