Technology-mediated simulation is often used in medical problem-based learning (PBL) approaches to offer authentic contexts and immersive engagement for learning. However, critiques argue that these approaches are lacking in the structure necessary to support productive learning--that they often result in mindless doing without the thinking processes needed that lead to deeper understanding and expertise. This paper presents data from a technology-mediated simulation, called HMS MEDscience, to demonstrate: (1) that it effectively leads to greater expert reasoning--evident through responses in content knowledge and problem-solving ability that more closely aligned with a rubric of expert responses to the same questions; (2) through a series of case studies, the implicit pedagogical moves the teachers make to support students' thinking processes. Significant pre- to posttest gains indicate more expert reasoning. In addition, classroom videos indicate shifts from novice toward more expert medical science reasoning and illustrate the fine-grained supporting moves that teachers use to guide students' thinking toward more expert understanding of the problem space. This study highlights the importance of the thinking processes that students engage in as they participate in technology-mediated PBL and the accompanying teacher attention to student thinking through supporting pedagogical moves.