Research pertaining to science museum exhibit design tends to be articulated at a level of generality that makes it difficult to apply in practice. To address this issue, the present study used a design-based research approach to understand the educational potential of a biology exhibit. The exhibit was considered an educational environment which embodied a certain body of biological knowledge (Biological Organisation) in a certain exhibit type (Museographic Organisation) with the intention of creating certain learning outcomes among visitors. The notion of praxeology was used to model intended and observed visitor outcomes, and the pattern of relationship between the two praxeologies was examined to pinpoint where and how divergences emerged. The implications of these divergences are discussed at the three levels of exhibit enactment, design, and conjecture, and theoretically based suggestions for a design iteration are given. The potential of the design-based research approach for educational exhibit design is argued. (Contains 1 note, 5 tables and 3 figures.)