We explore the integration of artificial intelligence (AI) into mathematics, science, and information class through three case studies in Korea and the United States. Drawing on the theoretical framework of AI as both a scaffold and a barrier, we examine how AI tools influence students’ cognitive processes and epistemic emotions—such as curiosity, confusion, and frustration, during inquiry-based learning. Our findings demonstrate that AI can enhance conceptual understanding, problem-solving, and emotional engagement when effectively mediated by teachers, but may also cause cognitive overload or dependency when misused. Cross-cultural comparisons reveal differing scaffolding strategies structured, concept-oriented approaches in Korea and open-ended, collaborative inquiry in the U.S. We emphasize the pivotal role of teachers as a mediator of human–AI interaction, emphasizing the need for pedagogical design that fosters student autonomy, emotional regulation, and critical AI literacy.