This chapter presents the randomized controlled trial that builds on insights from the design research study. It tests both the overall efficacy of the instructional design using an interactive video in the knowledge organization phase and the micro-design of its scaffolds: Highly structured scaffolds may promote students’ conceptual development more effectively than moderately structured scaffolds as they are more likely to focus students on subtle conceptual meanings. The sample comprised N = 239 students from remediation or lower-tracked classes who needed a second chance to understand algebra. Multiple linear regression analyses show that, for students who sufficiently used the provided learning opportunities, both video conditions—highly and moderately structured—outperformed a control group working with the same exploration tasks and worked example, but no instructional video. Although no significant differences emerged between the two video conditions, students using highly structured scaffolds demonstrated higher engagement with the learning opportunities.