We report on a cross-disciplinary collaboration between sociology and mathematics education to more effectively cultivate quantitative literacy (QL) in the introductory sociology course. Focusing on an instructional unit presenting the Gini coefficient (the most commonly used summary measure of income inequality), we engaged in iterative cycles of presentation, assessment, and redesign across four semester-long courses. Assessments were guided by insights from mathematics education--such as the procedural/conceptual distinction, student misconceptions, and student noticing--and characterized by extensive informal discussion and analysis of patterns in student exam responses. Assessments were formalized via coding of specific response elements and used to identify strategic foci for revision and redesign (including creating a brief instructional video series and an active learning exercise). In this article, we highlight the value of cross-disciplinary collaboration in QL pedagogy, demonstrate the effectiveness of analyzing specific elements and patterns of student comprehension to revise pedagogical presentation, and advocate for the strategic utility of the Gini coefficient for cultivating QL in introductory sociology.