Mathematics teachers are increasingly encouraged to incorporate computer-based technology in their classrooms, but these tools require strategic use in order to provide any substantive improvement to student understanding. This paper reports on how three middle-school mathematics teachers leveraged one particular tool, PhET interactive simulations (sims), quite differently. Using the perspective of instrumental orchestration, we describe five different sim and student roles that emerged in their lessons. These roles prompted different lesson orchestrations and varying opportunities for students to engage in the mathematics. Additionally, we present data from interviews with the teachers that document their beliefs about the affordances of PhET sims as we offer explanations for why each teacher orchestrated lessons differently. The interviews revealed each teacher’s preferred role in the classroom, demonstrating how tension between certain roles may inhibit the orchestration of an effective sim-based lesson. We conclude by sharing implications for sim-based mathematics instruction and teacher professional development.