Given the importance of vertical jump assessments as a performance benchmarking tool, the assessment of neuromuscular function and indicator of health status, accurate assessment is essential. This study compared countermovement jump (CMJ) height assessed using MyJump2 (JHMJ) to force-platform-derived jump height calculated from time in the air (JHTIA) and take-off velocity (JHTOV) in youth grassroots soccer players. Thirty participants (Age: 8.7 ± 0.42 yrs; 9 females) completed bilateral CMJs on force platforms whilst jump height was simultaneously evaluated using MyJump2. Intraclass correlation coefficients (ICC), Standard error of measurement (SEM), coefficient of variance (CV) and Bland–Altman analysis were used to compare performance of MyJump2 to force-platform-derived measures of CMJ height. The median jump height was 15.5 cm. Despite a high level of agreement between JHTIAand JHTOV(ICC = 0.955), CV (6.6%), mean bias (1.33 ± 1.62 cm) and 95% limits of agreement (LoA −1.85–4.51 cm) were greater than in other comparisons. JHMJperformed marginally better than JHTIAwhen compared to JHTOV(ICC = 0.971; 95% CI’s = 0.956–0.981; SEM = 0.3 cm; CV = 5.7%; mean bias = 0.36 ± 1.61 cm; LoA = −3.52–2.80 cm). Irrespective of method, jump height did not differ between males and females (p> 0.381;r< 0.093), and the comparison between assessment tools was not affected by sex. Given low jump heights achieved in youth, JHTIAand JHMJshould be used with caution. JHTOVshould be used to guarantee accuracy in the calculation of jump height.