The purpose of this 18-month case study is to highlight the successes and challenges that an ESL/mathematics teacher encountered as she made a shift from traditional mathematics curriculum to a standards-based curriculum as part of a statewide systemic initiative. The study was conducted in an urban, public middle school in Central Texas that served predominately low-income Latina/o students. The participant of this study was a middle school teacher who taught mathematics to English language learners in a self-contained classroom, which meant that 6th- through 8th-grade students were in the same classroom. Data sources included interviews, participant and nonparticipant classroom observations, fieldnotes, and documents. Three themes emerged from the data: (1) professional development opportunities and collaboration with a mainstream mathematics teacher, (2) change in teaching practices, and (3) equity issues. Findings indicate that this ESL/ mathematics teacher valued the professional development opportunities and collaborations with the mainstream mathematics teacher that supported her implementing a standards-based curriculum. The teacher also reflected on how her teaching changed by implementing units of the Connected Mathematics Project. However, a challenge she encountered with equity issues was the mismatch between the 6th-grade curriculum and the self-contained ESL classroom that consisted of 6th- through 8th-grade students. Other challenges were the lack of resources in the students' native language and the time needed to translate the curriculum materials. Implications and recommendations are discussed in relation to mathematics reform efforts in ESL classrooms. (Contains 2 notes, 1 table, and 1 figure.)