Purpose: The purpose of this study was to examine the process and outcome of an intervention using the project-based learning (PBL) model to increase students' health-related fitness (HRF) knowledge. Method: The participants were 185 fifth-grade students from three schools in Alabama (PBL group: n = 109; control group: n = 76). HRF knowledge was measured using a valid written test. Results: Using a two-level Hierarchical Linear Model (HLM) where students were nested within teachers' classrooms, the results show that controlling for "Class" there was a statistically significant difference between the two group conditions with the PBL cohort scoring 18.85% greater than the control schools at posttest. Discussion: The findings have shown supportive evidence as to the efficacy of a PBL-themed fitness education unit.