We examined the growth of teachers’ knowledge in the context of interdisciplinary teaching, which has been adopted by many educational settings in the last decade. Following teams of interdisciplinary teachers in design sessions for two school years, we sought to reveal what knowledge emerges and how it expands under these conditions. Our findings point to the need for a new framework to discuss knowledge growth outside of one’ discipline. We articulate the different knowledge components that emerged and offer a framework to capture teachers’ knowledge in interdisciplinary teaching model (KIT). This framework is sensitive to the context in which teachers work and can be useful to articulate teachers’ knowledge in other dynamic teaching and learning contexts.