This paper examines the role of positioning in the development of interactional competence of a Latino English Learner in a third grade mathematics classroom. Data is drawn from a three-year longitudinal study that examined the role of interaction in language and content learning for English Learners in content classrooms. Informed by positioning theory, this study draws upon multimodal analysis to provide microanalytic longitudinal mapping of the classroom interactional architecture, including the multimodal fluencies the student brings to bear on challenging interactions with peers. Findings suggest that the positioning practices constituting the classroom interactional architecture are inextricably intertwined with L2 learner access to classroom interactions that influence the trajectory of development of IC.