Mathematics curricula are often the primary resource used in the teaching and learning of mathematics--in particular, they represent mathematical knowledge for teachers and students. Yet, there seems to be a discrepancy between the curricular materials written for teachers and students (e.g., more variety in the semiotic choices in text provided for teachers than for students). This paper illustrates a way to compare the language written for the teacher and the student in curricula. Drawing on the social semiotic theory known as systemic functional linguistics (SFL), we examine what meaning potentials can be associated with the exchanges of knowledge proposed in mathematical text. Examining a Unit on Similarity in an online mathematics curriculum widely used in the United States, the paper explores how the semiotic systems in text presented for the teacher and student may impact the students' opportunity to learn and pose challenges in the instructional exchange between teacher and student. [For the complete proceedings, see ED657822.]