This study aims to compare the structural relationships among learning experiences (collaborative, active, and challenging learning), faculty and peer interactions, and college engagement between undeclared and declared-major students. Using data from the 2024 National Assessment of Student Engagement in Learning and Innovation (NASEL-i), multi-group structural equation modeling was conducted. The findings are as follows. First, collaborative and challenging learning indirectly enhanced engagement via faculty and peer interactions, whereas active learning increased engagement through faculty interaction but decreased it through peer interaction. Second, the path from challenging learning to faculty interaction was significant only among declared-major students, while the path from collaborative learning to peer interaction was significantly stronger among undeclared students. Moreover, faculty and peer interactions did not directly predict engagement, but mediated the effects of learning experiences. The study suggests supporting undeclared majors by fostering peer-based collaborative·challenging learning, assigning full-time faculty advisors, expanding feedback-centered active learning, and institutionalizing methods such as TBL and PBL.