Argumentative practices have been shown to deepen understanding and improve academic performance. After 10 years of work with science curricula designed to develop reasoning, we present a framework grounded in data from our projects for identifying different forms of metacognitive engagement in science inquiry classes. We focus on four categories of discourse from our data: object of thought or discourse; expressions of what someone is thinking; degree of specificity; and discourse applying and tailoring understanding of epistemic cognition to particular topics. We present multiple examples in each of these categories. Our goal is to provide analytic tools along with examples to better identify and code argumentative discourse that advances students' apt epistemic performance.