It is widely believed that school physical education (PE) is or, at the very least, can (even should) be a crucial vehicle for enhancing young people's engagement with physically active recreation (typically but not exclusively in the form of sport) in their leisure and, in the longer run, over the life-course. Despite the prevalence of such beliefs, there remains a dearth of evidence demonstrating a "PE effect". Indeed, the precise nature of the relationship between PE, youth sport and lifelong participation is seldom explored other than in implicit, often speculative and discursive, ways that simply take-for-granted the positive effects of the former (PE) on the latter (youth and adult participation in sport and physically active recreation). Using largely European studies to frame the issue, this article reflects upon the supposedly "causal" relationship between PE, youth sport and lifelong participation and, in doing so, highlights the inherent problems associated with attempts to identify, characterise and establish a "PE effect." In the process, the article points to a need for more longitudinal and biographical research exploring sports careers and the sporting habituses of young people, not least in order to better understand in precisely what circumstances PE interventions might work to enhance youth involvement in sport and physical activity and, subsequently, lifelong participation.