In this study, we evaluate the impact of rehearsing teaching skills in a mixed-reality classroom simulator on graduate teaching assistants' (GTAs) instructional practices as well as undergraduate student learning outcomes. The simulator training is intended to provide GTAs opportunities to deliberately practice essential pedagogical skills that support active learning, specifically in the context of the combined tutorial and laboratory sections of an algebra-based introductory physics sequence. Over three semesters, GTAs participated in different numbers of simulator rehearsal sessions: no simulator training, one session, and four sessions. We conducted 109 classroom observations for 23 GTAs, using a modified version of the Laboratory Observation Protocol for Undergraduate STEM (LOPUS); we also documented the frequencies of questioning-related skills (e.g., cold calling) implemented by the GTAs. Undergraduate student learning outcomes were measured by pre- and posttests of the Force Concept Inventory and Conceptual Survey of Electricity and Magnetism. We conducted hierarchical cluster analysis and found three instructional styles: the small-group facilitator, the whole-class facilitator, and the waiter. The results suggest that four-session simulator training throughout a semester supported GTAs (i) to shift away from the style of the waiter toward whole-class facilitator, and (ii) to implement posing questions and cold calling techniques. While new GTAs were found to have more interactive behaviors than experienced GTAs in the semester with no simulator training, we found that four-session simulator training supported both new and experienced GTAs to use more interactive instructional styles and implement questioning-related skills more frequently.