Background: Data storytelling is an interdisciplinary practice that uses visual and narrative elements to engage an audience with data. Students need more opportunities across school curriculum to consider the connections between data and social and environmental contexts. Few studies have investigated how to support teachers in co-designing for critical data storytelling and how engaging youth with photography might offer an entry point to critical data practices. Integrating data-inquiry practices with those in photojournalism, which has a history of challenging power by documenting lived experiences, has potential to support student engagement with critical data practices. In this study, I ask: 1) How do middle school teachers shift their practices as they co-design a critical data storytelling unit? and 2) How might data storytelling through the construction of photo-essays engage students with critical data practices? Methods: Over two years, we co-designed a five-week, 13-day critical data storytelling unit with one middle school teacher who taught art and physical education and a second teacher who taught math and ELA classes at a private school in the northeastern United States. There were 20 8th-grade students who participated in Year 2 of the study by generating data stories in the form of photo-essays. Data included 20 student photo-essays and a semi-structured interview with three students; post-implementation interviews with the art teacher and artifacts and transcripts from co-design meetings. Two researchers engaged in thematic analysis to identify mediating processes to explain 1) how the art teacher's practices around epistemic pluralism, shuttling between learning ecologies, and critical agency shifted between Year 1 and 2 of co-design and 2) how both data inquiry and narrative-art practices contributed to student engagement in critical data storytelling. Findings: Findings suggest that shuttling between disciplinary roles and using data and art tools to imagine student interactions during co-design were mediating processes that supported the art teacher in adopting epistemic pluralism and shuttling between learning ecologies as core design principles. In Year 2, we found that 12 students constructed data stories that drew on sensory imagery, exposition, and juxtaposition to engage with critical data practices. These data stories often argued for counting variables not represented in the large, civic data students explored and for operationalizing health indicators in ways that demonstrated epistemic pluralism. Contributions: This study contributes to existing literature that describes new contexts for data storytelling in K-12 education and describes mediating processes that contribute to teachers' professional development around this interdisciplinary practice. As a study of arts-integration, it contributes to an understanding of how photography as an artistic medium offers affordances for engaging students with critical data practices throughout a process of inquiry. Findings also contribute to an understanding of critical data practices by describing the role of narrative-art strategies as mediating processes for making sense of data as socially situated in a particular context and for generating opportunities to question how social and environmental issues are measured. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]