The influence of social relationships, positive interdependence, and teacher structure on the quality of partner reading interactions was examined. Partner reading, a scripted cooperative learning strategy, is often used in classrooms to promote the development of fluent and automatic reading skills. Forty-three pairs of second grade children were observed during partner reading sessions taking place in 12 classrooms. The degree to which the partners displayed social cooperation (instrumental support, emotional support, and conflict management) and on/off task behavior was evaluated. Children who chose their own partners showed greater social cooperation than children whose partners were selected by teachers. However, when the positive interdependence requirements of the task were not met within the pair (neither child had the skills to provide reading support or no one needed support), lower levels of on-task behavior were observed. Providing basic partner reading script instruction at the beginning of the year was associated with better social cooperation during partner reading, but providing elaborated instruction or no instruction was associated with poorer social cooperation. It is recommended that teachers provide basic script instruction and allow children to choose their own partners. Additionally, pairings of low ability children with other low ability children and high ability children with other high ability children should be avoided. Teachers may want to suggest alternate partners for children who inadvertently choose such pairings or adjust the text difficulty to the pair. Overall, partner reading seems to be an enjoyable pedagogical strategy for teaching reading fluency.