<p>Recent assessments of students’ reading comprehension in the United States have found that many 3rd, 4th, and 5th grade readers are not developing the skills necessary for academic success. iSTART-Early is an intelligent tutoring system that provides instruction on reading comprehension strategies and offers practice with skill application by answering review questions, designed to improve literacy outcomes. Across two studies, we measured students’ engagement, enjoyment, subjective difficulty, and objective difficulty of iSTART-Early lesson videos and review questions, by iteratively adapting and testing aspects of the system design based on findings. Study 1 revealed that the lessons were grade-appropriate for 3rd through 5th grade students regarding difficulty and enjoyment levels, with lessons being too simple for older children and too challenging for younger children. However, engagement was low across some lessons. In Study 2, modifications to iSTART-Early’s design were made based on Study 1’s findings, which were found to increase engagement while also maintaining appropriate enjoyment and difficulty levels for the target audience. Overall, these findings suggest that the design of lesson videos and review questions in iSTART-Early is grade-appropriate and has strong potential to enhance students’ reading comprehension skills.</p>