This study was designed to determine the fidelity of implementation (FOI) in a knowledge-based physical education (PE) curriculum using the 5E instructional structure. Utilizing a mixed-data method, observation checklist and fieldnotes data were gathered from 18 teachers' classes across 10 lessons of the 20-lesson curriculum. Results showed a substantial FOI variation across the 5Es segments. FOI was highest during Engagement and Exploration, with scores dropping as student-led learning increased in Explanation, Elaboration, and Evaluation. Lessons 8, 9, and 10, focused on energy catabolism and caloric balance, achieved the highest FOI rates. These findings underscore the importance of studying FOI, offer implications for examining FOI in PE, and provide a solid foundation for future research in this context.