A recent and important innovation in design-based research (DBR) is the use of conjecture maps, where researchers explicitly articulate the conjectured mediational relations between their designed goals and the learning designs and contexts. In this paper, we present a design case as an iterative sequence of evolving conjecture maps. As each conjecture map was tested, we revised it to highlight and refine our articulation of the tools and processes that embodied our design approach. Out design case involves small-town and rural community and school libraries in the United States as partners and DBR sites, with the goal of supporting librarians as they learn to develop and enact new STEM-oriented maker programs for youth. We show how conjecture mapping informed and supported our DBR work and how it helped push for specificity in hypothesized relations between the design, the learning setting, the outcomes. while also forcing a refection on design constraints.