This dissertation investigates youth science learning outcomes within the context of community and citizen science (CCS). In this unique educational context, youth learn about their local environment through data collection and then consider what to do with those data through environmental decision making. They also determine intellectual standards for what is “accurate enough” data and how to interpret their data and take action with it. Therefore, from science reasoning practices to environmental and civic action, CCS educational contexts can provide a rich forum to study youth agency and identity while doing and using science to make change. Chapter 2 and 3 focus on CCS learning outcomes in elementary schools. In Chapter 2, youth agency with data is investigated as one fourth-grader, Josefina, takes ownership of her data, manages her uncertainty and furthers her science inquiry to ensure accurate data. This chapter explores different variables which support youth perseverance within uncertainty, such as instructional framing about the tentative yet durable nature of knowledge. Findings from this chapter suggest that young people can develop sophisticated understandings about the nature of knowledge, which can in turn support youth in persevering with the uncertainty of inquiry and validity of data. In Chapter 3, fourth and fifth grade students participate in an afterschool CCS Ornithology Club and use their bird monitoring data to take action and imagine change on their school campus and beyond. This chapter illustrates how these young people contextualize their data within their first-hand experiences of making field observations. Therefore, as their individual interpretations of their observations vary based on their science content knowledge, values, and affective experiences during data collection, so too does the way in which they define campus-based environmental issues and their decisions for how to address them. This chapter highlights the importance of youth learning how to evaluate their interpretations and justifications. Both these ethnographic studies draw on data from student and teacher interviews plus field observations and considers implications for instruction and CCS project design. CCS project design is a main theme of Chapter 4. This literature synthesis draws on science and environmental education research to inform CCS project design for youth agency and for environmental action through science learning. Findings from these independent yet interrelated chapters are synthesized in Chapter 5, the Conclusion. Findings suggest that youth agency within CCS for science learning, intellectual rigor, and action is supported by youth 1) learning about the nature of knowledge and 2) engaging the data lifecycle, in which youth define questions, collect data and use those data for action and imagined change. As a whole, this dissertation argues for science education focused on place-based knowledge production, such as through CCS, as a means for youth doing and using science that is meaningful to them and their communities.