This case study considers how educational researchers and practitioners can work together to engage in "participatory knowledge building," a process rooted in both empirical research and the lived practices and expertise of on-the-ground educators that produces knowledge relevant to both educational theory and practice. The method shared was used as part of a broader approach called research-practice partnerships (RPPs), a model of collaboration between researchers and practitioners that departs from and counters traditional assumptions of "research translation" that suppose a unidirectional relationship where researchers simply share findings with educators, administrators, and youth. Instead, research-practice partnerships are characterized by joint work, mutuality, and a focus on persistent problems of practice across stakeholder groups. Within research-practice partnerships, we propose participatory knowledge building as one method that indexes these values. Rooting our case in the production of collaborative white papers addressing shared issues between researchers and practitioners, we first focus on "practical techniques" associated with participatory knowledge building, then discuss the "outcomes" of this approach for research-practice partnerships, and finally make "recommendations" for utilizing this approach. In discussing techniques to develop collective knowledge through participatory processes, we detail "topic emergence and selection," "leveraging community contexts as spaces for knowledge building," "integrating basic research data," "synthesizing and creating an initial draft of the paper," and "engaging in community-based feedback and dissemination." We then detail the outcomes that such a process has for those engaged in research-practice partnerships, including "development of shared language," "fostering a collective knowledge-building orientation," "surfacing practitioner expertise," "implicit renegotiation of the focus of joint work," and "catalyzing new educational experiments and shifts in practice." We close with lessons learned from our experience in this area and recommendations for others who are looking to engage in this practice. Broadly, the case highlights both the practicalities and affordances of using collaborative, participatory methods of knowledge production when the goal is first and foremost to improve educational practice. [This content is provided in the format of an e-book.]