Using Generative Artificial Intelligence (GAI) in education has opened new avenues for innovation, yet its role as an interactive tool with learners remains underexplored. Research in this domain faces challenges from pedagogical complexities and the variability of AI tools. To address these gaps, this study developed an online project-based learning (PBL) platform incorporating a GAI plug-in and conducted a year-long experiment to analyze its impact. Three sets of experimental analyses were performed to examine learners’ methods, cognitive processes, and learning effectiveness. The findings reveal that GAI significantly influenced students’ learning approaches, cognitive engagement, and learning effectiveness. Additionally, the study demonstrates that PBL offers an effective framework for investigating the educational implications of GAI, providing new insights for future research in this evolving field.