Mastery-based assessment is often implemented using binary pass/fail decisions; however, this approach can be insufficient in gateway mathematics courses such as College Algebra, where student understanding develops along a continuum. This interactive undergraduate research poster presents preliminary results from a faculty-collaborative study to design a mastery-based rubric that captures meaningful levels of algebraic understanding. Faculty participants evaluated authentic student work and identified distinguishing features across emerging mastery levels, informing the development of a multi-category mastery continuum. Poster visitors will engage directly with anonymized student responses by placing them along the proposed mastery continuum and comparing their classifications with faculty-derived levels. This activity highlights challenges in binary mastery judgments and illustrates how continuum-based rubrics can better support feedback, grading consistency, and instructional decision-making in early collegiate mathematics.