Background: Australia like many developed countries is largely an inactive nation. Participation in sport, a form of leisure-time physical activity, can contribute to a range of individual and community health benefits. National sport policy often has a dual focus on population-based participation, and elite performance. Whist there are various sport models depicting the pathway to elite, there has been no strategic population-level sport participation pathway model developed as a guide towards increasing sport participation. The aim of this study is to explore sport participation across age groups and develop a neutral (conceptual) model that does not favour community or elite sport and that highlights the critical participation transition points including drop-out, and specifically for children and youth. Methods: We conducted a longitudinal analysis of sport participation records for 8 major sports from 2015-2017 for children and young people aged 4-29 years. Individual participation within sports was tracked from 2015 and subsequent years 2016 and 2017. Results: The total number of participants was 579,696. Only half 50.8% played continuously for the three years, 44.7% dropped out, and 4.5 played discontinuously. Drop-out was highest for those aged 4 (57.0%), and lowest for those aged 10-14 years (39.3%). From the retention and drop-out participation patterns across the lifespan, in conjunction with the published literature on sport policy and participation, we developed the Sport Participation Pathway Model (SPPM). The SPPM conceptually depicts sport participation and in doing so emphasises the significant drop-out of sport. Conclusion: The retention data and the SPPM, demonstrates the trends in participation in sport and the high drop-out of competitive club-based sport. Those who manage and govern sport need to better recognise that club-based sport is merely one component of a range of leisure-time physical activities. If sport is to have an increased impact on making populations more active, then the evidence about the participation patterns and significant drop-out should be used to justify a re-focus on retention. We also recommend that the collection, analysis and reporting of longitudinal physical activity and sport participation data is expanded, to better serve policy evaluation and redirection.