The research on interpreting aptitude has focused on the abilities, skills and personal traits of individuals in order to predict their future interpreting performance. However, an important variable between the personal characteristics and success of trainee interpreters in interpreter training, which is instructional practices, is overlooked. Consequently, the different outcomes that were seen in trainees with various characteristics could be attributed to their adaptations to different instructional conditions. In order to address this gap in the literature, this exploratory study used the aptitude-treatment interaction (ATI) paradigm to examine the interactions between individual differences in trainee interpreters and feedback treatment. The findings of regression analyses suggested that working memory capacity predicted interpreting improvement under explicit and mixed feedback conditions rather than implicit conditions, and motivation predicted performance in the mixed group. Working memory capacity also predicted trainees' awareness in the explicit and mixed feedback groups, but not the implicit group. The results also showed that feedback awareness predicted interpreting progress, and error awareness predicted an improvement in the mixed group. Based on these findings, this study highlighted the importance of instruction-related factors in the relationship between aptitude and interpreter training success.