In this article Leinhardt demonstrates an analytic tool that can be used to trace the complexity of learning. Using “node-link diagrams” to look at the development of historical reasoning through one student’s writing from the beginning and end of the school year, Leinhardt highlights the multiple steps that go into constructing a reasoned analytic argumentative essay in history.  Arguing for the rigor of disciplinary standards for teaching history, the broader context for Leinhardt’s research is to understand how students process historical reasoning in order to inform the process of history teaching.