Conventional wisdom is that teachers have a model of teaching that they enact in the classroom. We studied middle school science teachers and found that the conventional wisdom does not explain large variations in practices for the same teachers in different contexts. During a study of PhET simulations, we observed two teachers in their regular (non-sim) classes and then in after-school classes in which they used PhET sims and activities developed by the PhET group. These activities were designed to be student-centered and inquiry-based. We find that one teacher led student-centered, inquiry-based activity in their regular classes but, in the after-school classes, controlled the classroom so that the sim activities were teacher-centered. The other teacher led teacher-centered regular classes, while enacting the sim activities in student-centered ways. We observe that teachers' practices can be significantly different across contexts, suggesting a sophisticated view of teacher practice is needed.