The present study aims to explore the cognitive processes of older students during their peer tutoring support of freshmen engaged in asynchronous discussion groups. Stimulated-recall was applied to study the underlying motives for specific tutor behavior in the online discussions and to make tutors' concerns explicit. A grounded theory approach was used to analyze the interview transcripts. A constant comparative analysis of the data resulted in six issues associated with peer tutors' cognitive processing in relation to actual tutoring behavior: strategy use, reasons for intervention, experience with online discussions, evaluation of faculty support, satisfaction with tutor-tutee interaction, and evolution over time. Furthermore, the results point at tutor worries. A major dilemma concerns the persistent problem of deciding when, how exactly, and how frequently to intervene. A second tutor dilemma is associated with the multidimensional tutor role. Thirdly, peer tutors struggle with the fact they are not professionals so not expert in the learning materials.