The presenters used a collaborative, design-based approach to improve teaching and learning in core courses in an online graduate program in Teacher Leadership. Specifically, they used Quality Matters peer reviews to improve the design of the core courses, and then made iterative improvements to course design and implementation across several semesters using the CoI survey. Results revealed this two-step process lead to significantly improved learning outcomes in three out of four core courses. The presenters will describe the course redesign process and how the CoI-based, iterative improvements were made. Research findings will also be presented.