CONTEXT: Neurocognitive testing is a recommended component in a concussion assessment. Clinicians should be aware of age and practice effects on these measures to ensure appropriate understanding of results. OBJECTIVE: To assess age and practice effects on computerized and paper-and-pencil neurocognitive testing batteries in collegiate and high school athletes. DESIGN: Cohort study. SETTING: Classroom and laboratory. PATIENTS OR OTHER PARTICIPANTS: Participants consisted of 20 collegiate student-athletes (age = 20.00 +/- 0.79 years) and 20 high school student-athletes (age = 16.00 +/- 0.86 years). MAIN OUTCOME MEASURE(S): Hopkins Verbal Learning Test scores, Brief Visual-Spatial Memory Test scores, Trail Making Test B total time, Symbol Digit Modalities Test score, Stroop Test total score, and 5 composite scores from the Immediate Post-Concussion Assessment and Cognitive Testing (ImPACT) served as outcome measures. Mixed-model analyses of variance were used to examine each measure. RESULTS: Collegiate student-athletes performed better than high school student-athletes on ImPACT processing speed composite score (F(1,38) = 5.03, P = .031) at all time points. No other age effects were observed. The Trail Making Test B total time (F(2,66) = 73.432, P < .001), Stroop Test total score (F(2,76) = 96.85, P = < .001) and ImPACT processing speed composite score (F(2,76) = 5.81, P = .005) improved in test sessions 2 and 3 compared with test session 1. Intraclass correlation coefficient calculations demonstrated values ranging from 0.12 to 0.72. CONCLUSIONS: An athlete's neurocognitive performance may vary across sessions. It is important for clinicians to know the reliability and precision of these tests in order to properly interpret test scores.