This introduction to the dissertation motivates and elaborates on its overarching research question: How can instructional videos enhance students’ conceptual understanding of a challenging algebra content? A conjecture map illustrates the dissertation’s structure: The design of a learning environment incorporating an instructional video is guided by two high-level design principles, namely supporting deep cognitive engagement and enhancing conceptual understanding. The dissertation refines these principles into mid-level design principles and design features, such as targeted interactive features that support students’ work with the video. Three cycles of design research are then employed to optimize the design, aiming to deepen students’ cognitive engagement and conceptual focus on relevant algebra content during the learning process. A randomized controlled trial tests whether the improved design promotes students’ conceptual understanding of variables and expressions, taking into account their use of the provided learning opportunities.