The purpose of this 2-part study was to explore the mathematical and purchasing competencies present in students' engagement in shopping practices in a low-income African American neighborhood. Study 1 consisted of in situ analyses of children's shopping activities at a local store, revealing the variety of arithmetic tasks that emerged in relation to varied artifacts, shopping routines, social norms, and clerk support. In an effort to reveal competencies that could not be measured through observation alone, Study 2 consisted of individual interviews of 30 first and second graders about tasks that required them to purchase items at a mock store. Analyses revealed both strategies that were frequently and infrequently associated with successful purchasing and the relationship between children's strategy choices and the demands of particular purchases. This research documents the many mathematical competencies children present that may not be captured in traditional school assessments and considers how this prior knowledge might be used to inform instruction and treatments of sociocultural frameworks.