This paper explores the effects of a collaborative, design-based approach to improving teaching and learning in core courses in an online program. It describes research which tested a model for linking iterative, theory based improvements in the design and implementation of online courses to learning outcomes. The researchers, who are also faculty in a graduate-level Teacher Leadership program, used the Quality Matters and Community of Inquiry frameworks to address first course design (QM) and then course implementation (CoI) issues across multiple semesters. Results show improved learning outcomes in most core courses from this two-step process.