Abstract: During the process of constructing scientific knowledge, scientists engage in the disciplinary work of looking for gaps between new data, existing theories, and phenomena in the world, and aim to respond to those gaps by designing and engaging in new investigations that aim to revise and improve upon existing knowledge. This process has been described as the work of problematizing (Engle & Conant, 2002; Phillips, Watkins, & Hammer, 2017; Reiser, 2004). Curriculum materials can be designed to support this disciplinary practice by seeding resources such as investigations, data, and phenomena into classroom instruction, but students need to be scaffolded into the work of identifying gaps between these resources and their existing knowledge in disciplinarily productive ways. In this talk, I examine the classroom discourse from one 6th grade classroom as they engage in 3 lessons over the course of a year. For each lesson, I identify 1) what resources are recruited to make sense of phenomena, 2) how these resources are used to problematize, 3) the types of problems are identified, and 4) the productive work is accomplished by identifying the gap. I will conclude the talk by discussing the implications of these findings for teacher learning.