In this study, three math and three science teacher educators (TEs) were positioned as designers of instruction. The investigation considered how TEs supported preservice teachers (PSTs) to learn to facilitate argumentation discussions using two digital simulations. Research questions were (a) How did TEs engage in instructional design around the simulations? and (b) What would TEs do differently if they were able to iterate in another semester? Using a convergent parallel mixed methods design, largely qualitative data were gathered, including from observations, surveys, written reflections, and interviews. An iterative, collaborative approach to qualitative data employed both a priori and emergent coding. Most TEs identified instructional goals and activities that focused on argumentation, questioning, disciplinary content, and student ideas. Half or more TEs cited these topics in their assessment of what PSTs learned. Overall, this study supports that positioning TEs as instructional designers is a contribution to the field's collective understanding of a pedagogy of teacher education. Further, the study may help researchers investigating TEs' instructional practices better understand the variability of contexts in which instructional design occurs and has implications for the types of supports designers of digital simulations could provide TEs.