Investigations into attrition of STEM-intending students indicate that poor experiences in introductory courses are at least partly to blame, specifically the students' frustration with lecture-driven teaching methods. In this research, hierarchical linear modeling is used to identify the individual and situational characteristics of instructors who support the use of student-centered pedagogy in Calculus I. Of specific interest are the effects of class size and perceived departmental support on an instructor's employment of student-centered pedagogical approaches. Overall, the effects of class size and support are functioning as the literature would suggest: instructors with large classes and minimal departmental support report lower usage of student-centered pedagogical approaches. The interesting finding is that these effects are more salient at the institutional level as compared with the instructor level. By analyzing national data gathered from 490 instructors distributed across 160 institutions, the findings of this research provide large-scale empirical support for several interview studies that have identified the importance of situational characteristics and highlight the importance of institutional context over the context experienced by individuals. Furthermore, this research suggests that change strategies might be more effectively supported through the department chair and/or course coordinators, as opposed to targeting individual instructors through professional development opportunities.