In this activity, students examine three student essays that are intended to persuade an audience regarding which of two models better explains a body of evidence. The essays differ along various dimensions such as number of pieces of evidence adduced to support the preferred model, the degree of elaboration in the description of the evidence, whether the writers explain how the evidence supports or contradicts the models, whether counterarguments are considered, (These essays can be taken from any prior unit and lesson that students are familiar with, and teachers can make them up based on common types of student essays. In our lessons, we have used essays from a lesson on mitochondria.) Students develop lists of ideas about what differentiates the essays in quality. Then teachers work through a series of powerpoint slides with the students, focusing on characteristics of good structural arguments. The activity culminates in the development of a rubric for evaluating argumentative essays--this rubric is discussed as one of our epistemic scaffolds.