The objective of this study was to determine the effect of physical exertion on computerized neuropsychological test performance in high school athletes as part of concussion return-to-play protocols. ImPACT data and consultation records were retrospectively reviewed among athletes undergoing their physical stepwise progression for return-to-play following sport-related concussion. Two hundred forty athletes met inclusion criteria and participated in the study. 36.7% of concussed athletes who were symptom-free and had reached an advanced stage of their return-to-play protocol demonstrated cognitive decline following a moderate level of physical exertion. Cognitive changes occurred on all four cognitive ImPACT composites after physical exertion. There was no difference with respect to post-concussive symptoms among within RCI (W-RCI) and below RCI (B-RCI) groups. Return-to-play protocols should include post-exertion neuropsychological testing, as relying on athlete symptom report will miss a significant portion of athletes who are continuing to recover from sport-related concussion, putting them at additional risk for repeat or catastrophic injury.