In this article, we offer theory-grounded narratives of a 4-year participatory design process of a Learning Analytics tool with K-12 educators. We describe how we "design-in-partnership" by leveraging educators' routines, values and cultural representations into the designs of digital dashboards. We make our long-term reasoning visible by reflecting upon how design decisions were made, discussing key tensions and analysing to what extent the developed tools were taken up in practice. Through thick design narratives, we reflect upon how cultural forms--recognizable cultural constructs that might cue and facilitate specific activities--were identified among educators and informed the design of a dashboard. We then examined the extent to which the designed tool supported coaches and teachers to engage in Generative Uncertainty, an interpretive stance in which educators manifest productive inquiries towards data. Our analysis highlights that attuning to cultural forms is a valuable first step but not enough towards designing LA tools for systems in ways that fit institutionalized practices, challenge instrumental uses and spur productive inquiry. We conclude by offering two key criteria for making culturally-grounded design decisions in the context of long-term partnerships.