Abstract: Meylan, CMP, Cronin, JB, Oliver, JL, Hughes, MG, McMaster, DT. The reliability of jump kinematics and kinetics in children of different maturity status. J Strength Cond Res 26(4): 1015–1026, 2012—The purpose of this study was to determine the reliability of eccentric (ECC) and concentric (CON) kinematic and kinetic variables thought to be critical to jump performance during bilateral vertical countermovement jump (VCMJ) and horizontal countermovement jump (HCMJ) across children of different maturity status. Forty-two athletic male and female participants between 9 and 16 years of age were divided into 3 maturity groups according to peak height velocity (PHV) offset (Post-PHV, At-PHV, and Pre-PHV) and percent of predicted adult stature. All the participants performed 3 VCMJ and HCMJ trials and the kinematics, and kinetics of these jumps were measured via a force plate over 3 testing sessions. In both jumps, vertical CON mean and peak power and jump height or distance were the most reliable measures across all groups (change in the mean [CM] = −5.4 to 6.2%; coefficient of variation [CV] = 2.1–9.4%; Intraclass correlation coefficient [ICC] = 0.82–0.98), whereas vertical ECC mean power was the only ECC variable with acceptable reliability for both jumps (CM = −0.7 to 10.1%; CV = 5.2–15.6%; ICC = 0.74–0.97). A less mature state was “likely” to “very likely” to reduce the reliability of the HCMJ ECC kinetics and kinematics. These findings suggested that movement variability is associated with the ECC phase of CMJs, especially in Pre-PHV during the HCMJ. Vertical CON mean and peak power and ECC mean power were deemed reliable and appropriate to be used in children as indicators of jump and stretch-shortening cycle performance.