This qualitative study examined the experiences of three eighth-grade prealgebra teachers as they planned student sensitive lessons for their ethnoculturally diverse students. The teachers worked in a lesson study group with a diversity consultant, an ESL (English as a second language) teacher who had a variety of multicultural experiences from around the globe. The findings of the study indicated that this form of student-sensitive lesson study stimulated in-depth mathematical discussions among participants and prompted a re-evaluation of the teachers' mathematical knowledge and practice. The diversity consultant supported the mathematics teachers in understanding their role in communicating mathematical content in ways relevant to their ethnoculturally diverse students. The role of lesson activity context to students' understanding and engagement and the need for closer attention to students' academic English-language proficiency when planning instruction surfaced as important elements for planning student-sensitive mathematics lessons. (Contains 1 table.)