This study explores the potential of social robots to contribute to reading motivation among children by examining usability issues and situational motivation. A prototype, Robot-Nils, was developed using the Furhat robot and a GPT-4o-based system to manage the dialogue. Fifty-four schoolchildren aged 11 to 12 interacted with the prototype, which was costumed and prompted to act as the main character from a book they had read. Participants interacted with the robot either individually or in groups. This was followed by interviews and a situational motivation questionnaire. Thematic analysis of video recordings and interviews identified four themes of usability issues: response time, politeness, information barriers, and insecurity. There were no statistically significant differences in motivation between individual and group conditions. Motivation was overall rated as moderate. The main design recommendation based on this study is to provide real-time feedback on speech recognition and response generation.