When addressing issues related to sport specialization, it is important to consider how skills are developed and learned. Changes in physical development and maturation throughout the growing years affect the motor performance abilities of individuals who are not yet mature. Such variability in skill development is important to understand when determining the impact of sport specialization on children and youths. This article addresses models of motor development that may be useful in examining the effects of sport specialization and discusses the variability of maturation among children during their growth years. (Contains 2 figures.)