This study, framed in theories of social semiotics, describes discipline-specific patterns of representation used across three disciplinesearth science, English, and mathematicsas they were taught by seven middle school teachers in the Southeastern United States. Under the assumption that each discipline would be characterized by distinctive patterns of representation because it addressed specific kinds of content, this study sought to (a) document those patterns; (b) speculate on why those patterns were prevalent in each discipline; and (c) describe reading and writing practices surrounding those patterns. Toward this end, the author observed the teachers for a total of 402 lessons ranging from 50 to 90 minutes each. Over the course of eight to nine months for each teacher, the author typed field notes of her or his instruction, took photographs of classroom artifacts such as handouts and whiteboard drawings, and conducted between four to nine interviews per person regarding representations used in the classroom. To describe the patterns of representation used in each discipline, the author and a colleague coded the data by identifying the types of representation that were used. To theorize what these particular types of representation might have afforded teachers and students across acts of communication, the author selected three video segments from instructional episodes in each discipline, based on their inclusion of the most common modes as indicated by the frequency count, and analyzed them using a multimodal concordance chart. The findings suggest that earth science relied heavily on gestures and a variety of iconic images as a means for representing movement and change on Earth; English relied heavily on written words as a means for addressing characteristics of language and intangible concepts such as characters motivation; and mathematics relied heavily on numeric symbolic combinations and abstract images, with gestures to point out connections between representations, as means for helping students visualize patterns and solve problems. The author describes specific reading and writing practices surrounding these modes and concludes with implications for disciplinary literacy instruction as the development of metarepresentational competence.