The moment many students begin to get excited about history is when they realize that much historical knowledge is contested, enmeshed in a productive argument that never ends and therefore endlessly fascinates. Such an epiphany might occur at any time. But a frequent catalyst is classroom debate, a formalized contest that dramatizes and vitalizes the challenge of constructing historical knowledge. A central problem for many instructors, therefore, is to design debates that enhance the engagement of all students, both those involved directly in debate and those who listen actively. This article describes how, with the help of Mark Vincent, a psychologist with expertise in cognition and statistical analysis, historian David Ellis turned student-led debates from the weakest to one of the strongest links in his courses through introducing both a structured controversy format and elements of liminal and ludic learning. Data collected over several years demonstrate broad gains in historical and critical thinking in all measured categories. All student groups saw gains, and in comparison to a more traditional debate format, the structured controversy format moved closer to parity in gains among men and women.