Background: The expanded use of online and blended learning programs in K-12 STEM education has led researchers to propose design principles for effective e-learning systems. Much of this research has focused on the impact on learning, but not how instructional design impacts student engagement, which has a critical impact both on short-term learning and long-term outcomes. Reasoning Mind has incorporated the e-learning principles of personalization, modality, and redundancy into the design of their next-generation blended learning platform for middle-school mathematics, named Genie 3. In three studies, we compare student engagement with the Genie 3 platform to its predecessor, Genie 2, and to traditional classroom instruction. Results: Study 1 found very high levels of student engagement with the Genie 2 platform, with 89 % time on-task and 71 % engaged concentration. Study 2 found that students using Genie 3 spent significantly more time in independent on-task behavior and less time off-task or engaged in on task conversation with peers than students using Genie 2. Students using Genie 3 also showed more engaged concentration and less confusion. Study 3 found that students using Genie 3 spent 93 % of their time on-task, compared to 69 % in traditional classrooms. They also showed more engaged concentration and less boredom and confusion. Genie 3 students sustained their engagement for the entire class period, while engagement in the traditional classroom dropped off later in the class session. In both study 2 and 3, Genie 3 students showed more growth from pre- to post-test on an assessment of key concepts in sixth-grade mathematics. Conclusions: The incorporation of evidence-based e-learning principles into the design of the Genie 3 platform resulted in higher levels of student engagement when compared to an earlier, well-established platform that lacked those principles, as well as when compared to traditional classroom instruction. Increased personalization, the use of multiple modalities, and minimization of redundancy resulted in significant increases in time on-task and engaged concentration, but also a decrease in peer interaction. On the whole, this evidence suggests that capturing students' attention, fostering deep learning, and minimizing cognitive load leads to improved engagement, and ultimately better educational outcomes.