The REAP tutoring system provides individualized and adaptive English as a Second Language vocabulary practice. REAP can automatically personalize instruction by providing practice readings about topics that match interests as well as domain-based, cognitive objectives. While most previous research on motivation in intelligent tutoring environments has focused on increasing extrinsic motivation, this study focused on increasing personal interest. Students were randomly split into control and treatment groups. The control-condition tutor chose texts to maximize domain-based goals such as the density of practice opportunities for target words. The treatment-condition tutor also preferred texts that matched personal interests. The results show positive effects of personalization, and also demonstrate the importance of negotiating between motivational and domain-based goals.