Background/Context: Young children's engagement with mathematics is occurring in a context in which school transition and readiness concerns that invoke increased institutional rules and disciplinary practices involving power dynamics are coming into play. These trends made us curious to undertake an in-depth investigation of the different ways children and their teachers engage in mathematics in preschool classrooms today. Purpose/Focus of Study: In our video-ethnography study we explored the ways mathematics manifested itself in a Pre-K setting and how mathematics functioned in different ways throughout the school day. The question guiding our research was: Recognizing the context of current transition and readiness concerns in early childhood education, in what ways is mathematics manifested in the interactions of teachers and children in a Pre-K classroom? Setting: The study took place in a childcare center, accredited by the National Association for the Education of Young Children, in the United States. Participants: Participants in this study were four 4- to 5-year-old children and their teachers in an ethnically diverse classroom. Research Design: The study drew on a video-ethnographic method through semester-long observations and video-recordings in a Pre-K classroom. The analysis began with (a) labeling manifestations of mathematics in the video data through open coding, proceeded to (b) the examination and the categorization of the various manifestations of mathematics, was followed by (c) the identification of the key scenes which best represented each category, and ended with (d) the multimodal analysis of the key scenes. Findings: This research illustrated that formal mathematics teaching and learning contexts included the kinds of disciplinary and bodily control practices that have been evident in studies of children at the preschool level transitioning into school. The study demonstrated the ways that mathematics, with its authoritative and classificatory nature, became a disciplinary tool itself during the course of the day. Also evident were the ways in which all actors in the classroom drew on mathematics for problem-solving in real-life situations within a power/resistance dynamic. Conclusions/Recommendations: This research raises questions of how disciplinary practices might limit children's mathematics learning. The finding that mathematics was implicated in the practices of power dynamics among teachers and children and among children opens up possibilities for teachers to recognize how mathematics is being used informally and creatively by children. Teachers can then use this knowledge to build on young children's identities as powerful and competent mathematicians, using mathematics in problem solving during day-to-day interactions.