This paper explores a contrast between two strategies of intervention research. The first strategy, referred to as design experimentation, came to prominence through the writing of Ann Brown and Allan Collins. Design experiments were described as attempts to engineer innovative learning environments and simultaneously understand salient aspects of human cognition and learning. The core of the method is to place a version of a learning design into the world and iteratively revise the design in light of results from each implementation. The second strategy is referred to as mutual appropriation, a term used by Newman, Griffin, and Cole to describe teaching/learning processes in classrooms, but subsequently introduced into the intervention literature by Brown and Campione to describe an intervention process in which the nature of the intervention is not pre-specified, but negotiated among participants over time. We endeavor to show that a mutual appropriation approach can help the field create interventions which are themselves developmental in their fundamental methodology.