The Design Implementation Framework, or DIF, is a design approach that evaluates learner and user experience at multiple points in the development of intelligent tutoring systems. In this chapter, we explore how DIF was used to make system modifications to iSTART, a game-based intelligent tutoring system for reading comprehension. Using DIF as a guide, we conducted internal testing, focus groups, and usability walk-throughs to develop iSTART-3, the latest iteration of iSTART. In addition to these evaluations, DIF highlights the need for experimental evaluation. With this in mind, we describe an experimental evaluation of iSTART-3 as compared to its predecessor, iSTART-ME2. Analyses revealed an interesting tension between system usability and user preference that has important implications for instructional designers. [This chapter was published in: M. Schmidt, A. A. Tawfik, I. Jahnke, & Y. Earnshaw (Eds.), "Learner and User Experience Research: An Introduction for the Field of Learning Design & Technology." EdTech Books.]