Ambitious mathematics instruction has emerged as a response to persistent inequities in mathematics classrooms, where students who struggle are often excluded from meaningful engagement. This paper is methodological in nature and situated in the critical preparatory phase of an intervention within an Educational Design Research (EDR) project. Rather than presenting empirical results, the paper explores how two theoretical frameworks -teachers’ instructional visions (Munter, 2014) and teachers’ self-efficacy (Bandura, 1997) -can be operationalized as meta-design principles to inform the planning of an intervention in co-teaching settings. Teachers’ instructional visions offer a normative orientation towards high-quality and inclusive instruction, while teachers’ self-efficacy provides a pragmatic focus on teachers’ perceived capabilitiesfor action. Together, these frameworks suggest how interventions can begin from where teachers currently are and at the same time create opportunities for sustainable shiftsin practice. Design principles such as talk moves and proactive support are discussed as concrete entry points that both align with teachers’ existing instructional visions and support a reimagining of inclusion. That is moving from participation as presence towards participation as valuing diverse student thinking. By positioning these frameworks as complementary lenses in the design phase, this paper contributes a methodological proposal for how theory can be operationalized to bridge equity-oriented aspirations with the realities of teacher learning in professional development for ambitious mathematics instruction.