Open data offers the potential to enhance citizen participation, transparency, and accountability in society. However, a lack of competencies that enable citizens to engage in open data ecosystems remains a barrier. Although authentic open data inquiry has been identified as a promising approach to develop open data learning designs in schools, its connection to open data competencies is not yet well understood. To advance the understanding of open data competencies and learning designs, this study focuses on the inductive analysis of two design-based research cycles and four interventions in Danish schools. A cohort of 7th to 9th grade pupils (n = 78) and their teachers (n = 4) engaged with The Open Data Newsroom, an open data learning design that situates pupils in the role of data journalists to solve an environmental mystery. Following a thematic analysis approach, we examined qualitative data from observations, surveys, and interviews to identify four categories that encompass pupils’ practices for (1) navigating open data: find and assess relevant information and data to identify a problem; (2) developing authentic open data analysis: analyse and interpret data in connection to real-world problems and local contexts; (3) building authentic data arguments and stories: explain a problem with data from different sources and domains to lay audiences; and (4) creating open data representations: build tools to support inquiry and communication. We argue that these practices, grounded in data literacy and real-world problem solving, contribute to defining open data competencies in schools, and we present a model to illustrate this connection.