This article centers sociocultural and sociopolitical considerations of how young people understand, represent, and use data by presenting findings from a social design research study about how students in a public urban high school authored "data stories" using personal data they curated, collected, and visualized. The study contributes to theoretical understandings of critical data literacies by considering the experiences and practices of adolescents enrolled in a required media arts class as they produced data visualizations drawn from their everyday lives. Findings center on two aspects of critical data literacies youth developed--understanding themselves as people capable of using data for multiple purposes and understanding data as socially situated resources for meaning-making. This study foregrounds the importance of positioning youth as authors and architects of data, making central youth perspectives in understanding the role of data in young people's digitally connected lives and highlighting the importance of expanding what "counts" as data. It also suggests the importance of creating infrastructure to support the development of culturally relevant data practices that highlight the social, cultural, and political uses of data and its racialized dimensions.