What goes into faculty decisions to adopt a classroom intervention that closes achievement gaps? We present a theoretical model for understanding possible resistance to and support for implementing and sustaining a diversity-enhancing classroom intervention. We propose, examine, and refine a "diversity interventions--resistance to action" model with four key inputs that help explain faculty's decision to implement (or not) an evidence-based intervention: (1) notice that underrepresentation is a problem; (2) interpret underrepresentation as needing immediate action; (3) assume responsibility; and (4) know how to help. Using an embedded mixed-methods design, we worked with a sample of 40 biology faculty from across the United States who participated in in-depth, semistructured, qualitative interviews and surveys. Survey results offer initial support for the model, showing that the inputs are associated with faculty's perceived value of and implementation intentions for a diversity-enhancing classroom intervention. Findings from qualitative narratives provide rich contextual information that illuminates how faculty think about diversity and classroom interventions. The diversity interventions--resistance to action model highlights the explicit role of faculty as systemic gatekeepers in field-wide efforts to diversify biology education, and findings point to strategies for overcoming different aspects of faculty resistance in order to scale up diversity-enhancing classroom interventions.