Assessing Interactional Competence Through Generative AI: Comparing Large Language Models as AI Interlocutors in the Paired Oral Discussion Test

Interactional competence (IC) is essential for oral communication assessment, yet human partner variability can introduce construct-irrelevant variance in paired speaking tests. As an alternative to a test with a human interlocutor, this study describes the development of a large language model (LLM)-driven Spoken Dialogue System and compares GPT-4o to Claude 3.5 Sonnet to inform model selection for IC assessment. Twelve international students completed paired discussion tasks with both LLMs in counterbalanced order. System performance was evaluated through breakdown activation consistency, stance maintenance, and persona adherence. Test-taker performances were analyzed using interactional discourse analysis to identify IC features across three dimensions: topic management, interactional management, and interactive listening. Semi-structured interviews explored test takers’ perceptions of the AI partners. Results showed Claude outperformed GPT-4o in eliciting IC features, successfully activating communication breakdown strategies and maintaining oppositional stance, thereby creating more opportunities for test takers to demonstrate key IC abilities. Test takers perceived Claude as more authentic and natural, while GPT was perceived as more artificial. These findings demonstrate that different LLMs create distinct interactional conditions affecting both IC elicitation and test-taker perceptions. The findings highlight the need for construct-driven evaluation criteria when selecting LLMs for language-assessment contexts.