There is an ongoing need to support students' learning of linear functions, and the study of slope makes up a foundational component of this learning. We applied techniques from systemic functional linguistics to document the meanings that were established through spoken interaction between a student and her tutors during discussions of slope. We found that, while fraction notation gave the student and tutors a common reference point to discuss slope, it also masked important differences in how the student interpreted slope compared to her tutors. The findings of this analysis imply the need not only to attend to how students quantify slope, but also whether students recognize slope as an attribute of a line.