Adaptive Instructional Systems (AISs) support learners by adapting a variety of features depending on learner performance and characteristics. A common adaptive intervention is to change the difficulty of the training to maintain an appropriate difficulty level for learners. However, changes in task load have been shown to increase stress in learners. Given the ubiquity of adaptive difficulty and the established detrimental effects of stress on performance, the interplay of adaptive difficulty and stress is under-investigated in AIS literature. The transactional model of stress emphasizes the role of stress appraisal and coping strategies in the stress-performance relationship. This study extends previous research by examining how stress appraisal and emotion-focused coping (EFC) influence task performance in a demanding electronic warfare (EW) task. We explore the role of behavioral markers as indicators of stress responses and discuss their value as an adaptive variable. Results suggest that stress appraisal affects performance indirectly by affecting coping, slowing task behaviors, and subsequently degrading task performance. Our findings suggest that incorporating behavioral markers of stress responses into adaptive instructional systems (AISs) provides a non-intrusive method for real-time stress assessment, allowing for dynamic adjustments to adaptive instruction. These findings offer practical insights for AIS design, highlighting the importance of monitoring stress-related behaviors to optimize learning and performance outcomes. The present work discusses the importance of identifying theoretically relevant models and variables for AIS design and demonstrates the identification of a generic variable associated with stress and performance.