Three community college faculty members used improvement science techniques to design, develop, and refine contextualized developmental mathematics lessons, where language and literacy pedagogy and related supports figured prominently in these instructional materials. This article reports on the role that their design experiences played in professional learning. The article uses a model of professional learning developed by Clarke and Hollingsworth (2002) as the lens to describe and analyze their experiences. Results indicated theoretically noteworthy variation among the faculty. The results highlight a strong connection between faculty willingness to experiment, during trial enactment of these lessons, in their classrooms and faculty growth in knowledge and belief structures about the importance of language and literacy to mathematics teaching and learning. Implications for design-based development, as an important ongoing professional development activity for mathematics instructors, are discussed.