CONTEXT: Increased sport participation and sport-related concussion incidence has led to an emphasis on having an appropriate medical professional available to high school athletes. The medical professional best suited to provide medical care to high school athletes is a certified athletic trainer (AT). Access to an AT may influence the reporting of sport-related concussion in the high school athletic population; however, little is known about how the presence of an AT affects concussion knowledge, prevention, and recognition. OBJECTIVE: To evaluate knowledge of concussion and reporting behaviors in high school athletes who did or did not have access to an AT. DESIGN: Cross-sectional study. SETTING: Survey. PATIENTS OR OTHER PARTICIPANTS: A total of 438 athletes with access to an AT and 277 without access to an AT. INTERVENTION(S): A validated knowledge-of-concussion survey consisting of 83 items addressing concussion history, concussion knowledge, scenario questions, signs and symptoms of a concussion, and reasons why an athlete would not report a concussion. The independent variable was access to an AT. MAIN OUTCOME MEASURE(S): We examined the proportion of athletes who correctly identified knowledge of concussion, signs and symptoms of concussion, and reasons why high school student-athletes would not disclose a potential concussive injury by access to an AT. Frequency statistics, χ2 tests, independent t tests, and linear regression were conducted to analyze the data. RESULTS: The underreporting of concussion among high school athletes was 55%. Athletes with access to an AT had more knowledge of concussion than did athletes without such access (P ≤ .001). Chi-square tests did not demonstrate a significant relationship between AT access and a higher percentage reporting concussions. CONCLUSIONS: High school athletes with access to an AT had more concussion knowledge, but they did not report suspected concussions to an authority figure more frequently than athletes without access to an AT.