Evidence-based instructional methods (EBIMs) increase student learning outcomes in undergraduate geoscience classrooms (Freeman et al., 2014). Borrego, Stains, and colleagues estimate that only 40-50% of instructors employ EBIMs in their STEM classrooms (Borrego et al., 2010; Stains et al., 2018). It is still unclear what drives instructors to adopt or not adopt EBIMs. This study investigates the following research question: What is the relationship between attending teaching-focused professional development (PD) programs and instructors' decisions on whether and how to implement EBIMs? Triadic reciprocal determinism (TRD) (Bandura, 1971) is used as a theoretical framework in this study to explore the connections between personal, environmental, and behavioral factors. This study uses the methodology of a multiple-case study. Data collection methods involved Zoom-based interviews. Data was coded with a priori defined factors from the TRD model. Interview data reveals that a complex interaction between all three factors is involved in an instructor's decision to attend PD and their decisions on whether to implement EBIMs after participating in PD programs. From the interview data, key components of each of the three TRD factors were identified as barriers or catalysts to implementing EBIMs after participating in PD programs. Recommendations are made for how to build stronger PD programs that address the barriers that instructors face when attempting to implement EBIMs after attending PD programs.