For many years, sport researchers have warned about the lack of a clear and consistent definition of early specialization (Buckley et al., 2017; Ferguson & Stern, 2014), while others have raised concerns around the validity of current methods used to classify athletes as 'specializers' (Smith et al., 2017). To this end, this investigation includes two studies aimed at examining the implications of variable classification methods for exploring both specialization and early specialization in sport. Study 1 examined how different approaches to defining and measuring specialization affected the classification of athletes throughout development and provided a 'profile' of the sample in terms of developmental milestones related to specialization. Participants included 362 athletes from a variety of sports. Results indicated that the proportion of athletes classified as specializers varied depending on the definition/method used and that athletes were meeting specialization milestones after the age of 12. Study 2 examined the proportions of athletes who achieved 'elite', 'pre-elite' and 'non-elite' status in adulthood who were early specializers as determined by each method/definition and compared those who were specializers to non-specializers using each method/definition to determine the proportions who developed into 'elite' athletes. Participants included all athletes from study 1 who were over the age of 18 (n= 237). Results showed that the method/definition used changed the proportion of athletes classified as specializers at each level and that there was no clear advantage or disadvantage to being a specializer. Combined, these studies highlight several important implications from the use of different definitions/measures of specialization.