Rubrics’ relation to language teacher beliefs and decision-making remains under-researched. This mixed-methods study examined longitudinal data from L2 Spanish instructors (The terms “teachers” and “instructors” will be used interchangeably to avoid redundancies) in U.S./Canadian higher education settings. Instructors (N = 33 in each Phase 1 and Phase 2) completed surveys about rubric implementation—exploring attitudes, perceived benefits/drawbacks, institutional dynamics. Follow-up interviews (N = 6 each Phase) illuminate their preferences and agentive negotiations when developing, implementing, and adapting rubrics. Results showed teachers valued rubrics’ contributions to grading fairness, consistency, and transparency, helping build shared assignment expectations and connections to feedback. However, some teachers felt rubrics could restrict students’ writing creativity. Regarding different rubric types, analytic ones were favored for specificity and clarity, facilitating more objective, multi-faceted evaluation of writing, yet often seen as time-consuming. Holistic rubrics were valued as efficient in low-stakes tasks, yet potentially subjective. The study also explored teachers’ evolving agency within institutional ecologies/systems, illustrated by a continuum of agentive curricular stances—spanning from strong programmatic consistency, to flexible consistency, and finally consistent flexibility. Implications for professional development, and teacher education include advocating for assessment literacy and training to navigate affordances/constraints of implementing rubrics within situated contexts.