ABSTRACT This article presents results from a design experiment intended to develop students’ understanding of linear functions and rates of change in a linguistically diverse ninth grade classroom. The intervention focused on fostering classroom discussions. Students’ pre-post assessment gains were higher in the redesigned classrooms than in the pre-intervention classrooms. Additionally, multilingual students who were classified as English Learners (ELs) made larger gains than their non-EL peers, and the majority of student learning gains occurred on conceptually-focused items. Analysis of classroom talk showed an increase in high demand moves from the teacher and an increase in the level of teacher responsiveness to students’ mathematical ideas. We discuss implications for future research and design efforts to enhance student learning in multilingual mathematics classrooms.