Researchers and developers of learning analytics (LA) systems are increasingly adopting human-centred design (HCD) approaches, with growing need to understand how to apply design practice in different educational settings. In this paper, we present a design narrative of our experience developing dashboards to support middle school mathematics teachers' pedagogical practices, in a multi-university, multi-school district, improvement science initiative in the United States. Through documentation of our design experience, we offer ways to adapt common HCD methods -- contextual design and design tensions -- when developing visual analytics systems for educators. We also illuminate how adopting these design methods within the context of improvement science and research-practice partnerships fundamentally influences the design choices we make and the focal questions we undertake. The results of this design process flow naturally from the appropriation and repurposing of tools by district partners and directly inform improvement goals.