The evaluation of promisingness is central to knowledge buildingand knowledge creation but remains largely unexplored. As partof a design-based research program to support promisingnessjudgments, the present study implemented an intervention in asixth grade science class, with the goal of exploring thepotential of promisingness judgments to foster scientificunderstanding and epistemic beliefs. Aided by a Promising IdeasTool and pedagogical supports designed for this intervention,students explored the concept of promisingness, judged thepromisingness of their community ideas, and engaged in iterativecycles of idea refinement. Results indicated that students werecapable of improving their understanding of promisingness andmaking promisingness judgments deemed sensible by domainexperts. The conceptual understanding and epistemic beliefsdisplayed by students improved over the course of theintervention, and such improvement happened in tandem withstudents’ understanding of promisingness. The implications ofthis exploratory study and future research are discussed.