The need for concussion-related safety programs in high-school athletics is well recognized. To that end, valid-baseline assessments are compulsory in order for medical staff to identify athletes suspected of having a concussion and best inform appropriate medical-treatment protocols. PURPOSE: To determine the between-trial reliability of the King-Devick Test (KD) as part of a pre-season concussion-safety program in young-male high-school athletes. METHODS: KD baseline score data from high-school, male athletes (n = 377, aged 16 ± 1 years) were recorded on electronic tablets and later analyzed. The testing required participants to complete two, error-free trials, which were reported to the nearest 0.0 s. For both trials, descriptive data were reported, mean differences were examined via paired-samples t-tests, Cohn’s d effect sizes were considered, and two-way mixed-effects intraclass correlations (ICC) were implemented. RESULTS: The KD test showed strong reliability between trials (Trial 1 = 56.0 ± 15.2 s; Trial 2 = 53.3 ± 13.8 s; single-measure ICC = 0.93; 95% CI 0.91 - 0.94). Furthermore, similar reliability was observed when KD scores were grouped by Best score and Worst score (Best = 52.8 ± 13.6 s; Worst = 57.6 ± 15.3 s; single-measure ICC = 0.95; 95% CI 0.94 - 0.96). Paired-samples t-test identified small-differences between both pairings (Trail 1 vs. Trial 2, p < 0.001, d = 0.25; Best vs. Worst, p < 0.001, d = 0.33). Most participants (78.5%) recorded their Best score on Trial 2. CONCLUSIONS: The KD test showed excellent reliability between trials in this population of young-male athletes. However, additional research is warranted with respect to how many valid baseline attempts are needed to acquire a stable KD score to best support safe-monitoring practices.