Maintaining learner engagement is critical for all types of learning technologies. This study investigated how choice over a learning topic and the difficulty of the materials influenced mind wandering, engagement, and learning during a computerized learning task. 59 participants were randomly assigned to a text difficulty and choice condition (i.e., self-selected or experimenter-selected topic) and measures of mind wandering and engagement were collected during learning. Participants who studied the difficult version of the texts reported significantly higher rates of mind wandering (d =.41) and lower arousal both during (d =.52) and after the learning session (d =.48). Mind wandering and arousal were not affected by choice. However, participants who were assigned to study the topic they selected reported significantly more positive valence during (d =.57) but not after learning. These participants also scored substantially higher on a subsequent knowledge test (d = 1.27). These results suggest that choice and text difficulty differentially impact mind wandering, engagement, and learning and provide important considerations for the design of ITSs and serious games with a reading component.