Background Deep neck flexor (DNF) muscles stabilize the neck and contribute to head acceleration control. The function of DNF in cervical spine dynamic stabilization has not been examined in athletes of any age group, including adolescents. This investigation was necessary prior to studying the DNF muscles' role in cervical spine injury patterns. Objectives The objectives of this study were (1) to determine average Deep Neck Flexor Endurance Test (DNFET) time scores in high school−aged and university‐aged subjects (aged 14‐22 years); and (2) to establish the relationship between gender and age for adolescent DNFET time scores. Design Cross‐sectional design. Setting Public high school and private university. Participants A total of 81 (40 male, 41 female) healthy high school and collegiate athletes. Intervention DNFET time scores (in seconds) were collected and means values were calculated. Interrater reliability was established using the first 15 university‐aged subjects enrolled in the study. Main Outcomes Mean DNFET time (seconds) scores. Results The DNF muscle endurance interrater reliability coefficient of reproducibility for 4 allied health clinicians was intraclass correlation coefficient (2,4) 0.712 (confidence interval, 0.24‐0.85). The mean (± standard deviation) DNFET time score for females was 31.86 (±8.53) seconds versus 35.57 (±10.43) seconds for males. The DNFET performance demonstrated a significant but fair correlation with age (r = 0.401, P = .0001). No significant performance differences were found between male and female subjects in the 14‐ to 17‐year‐old group (U = 187.0, P = .285), the 18‐ to 22‐year‐old group (U = 145.0, P = .215), or the total male versus female subject groups (U = 653.0, P = .083). Conclusion Our study establishes a normative data set available for the DNFET in the adolescent population. The fair correlation between DNFET time scores and age is consistent with other studies. These findings serve as a basis for clinician testing, objectifying, and monitoring DNF dysfunction in an adolescent athletic population. Level of Evidence II