This study investigated how eleven secondary mathematics teachers used curriculum resources to plan and enact lessons that support the participation of emergent bilingual (EB) students in mathematical practices in their linguistically diverse classrooms. EB students classified as English Learners often experience mathematics as a set of disconnected procedures. This investigation was rooted in a situated sociocultural theory of learning (Moschkovich, 2002) and a conceptual framework for the teacher-curriculum interaction (Remillard, 2005, 2009). This study was designed to answer the following questions: (1) How do curriculum materials provide supports for engaging emergent bilingual students in mathematical practices? and (2) How do teachers in linguistically diverse classrooms use curriculum materials to plan and enact lessons that support emergent bilingual students’ engagement in mathematical practices? The study used a contrastive design, examining both the official curriculum and teacher- created materials used by teachers in two districts that adopted different Common Core-aligned curricula. The official curricula provided different types of guidance for teachers to support EB students. The eleven participating teachers, six from School A and five from School B, participated in a lesson planning interview (Grossman, 1990), a classroom observation, and a debriefing interview. Data analysis included inductive and deductive coding, using a priori codes based upon the CCSSM Standards for Mathematical Practice (NGA & CCSSO, 2010), the English Learners Success Forum’s Guidelines for Improving Math Materials for ELs (ELSF, n.d.), and research on supporting English Learners (Chval, Pinnow, & Thomas, 2015). Some of the main findings of this investigation include the following. (1) The participating teachers held varying interpretations of the eight CCSSM Standards for Mathematical Practice, leading to a wide range of enactments of the same practice standard across classrooms. (2) The participating teachers were not using curriculum materials in their published forms. Teachers cited text difficulty and the difficulty their linguistically diverse students had with reading the textbooks as a rationale for modifying the written curriculum. (3) Despite these variations in enactment, all participating teachers expressed similar care and concern about the success of their students and believed that they were doing exactly what their students need to learn mathematics.