This paper explores the influence that school sport and non-sport extracurricular activities (ssEC and nsEC) can have on academic achievement. A central thesis of this paper is that, despite the literature on the perceived and presumed benefits of school sport and of non-sport activities, theorising a model of the process by which the benefit is attained, which we conceptualise as a case of transfer, has been neglected. Cognisant of the long-standing literature on transfer and the recent resurgence in transfer research, we present a dual step transfer hypothesis by which ssEC and nsEC activities confer academic achievement benefits. Key to this dual step transfer hypothesis is the influence these activities have on non-cognitive skills, whereby the activity promotes non-cognitive skills (i.e., motivational-social skills), which in turn promote learning and academic achievement. We present an overview of transfer from the early discussions framing transfer to either mental muscle or identical elements mechanisms, to more recent discussions and new perspectives on what counts as transfer. To this discussion we compare research linking academic achievement to school physical education, school sport and school non-sport activities. We place particular emphasis on extracurricular activities and the potential influence they can have on non-cognitive characteristics. In making our argument we weigh up the relative support for dual step transfer within extant literature on both areas, and in doing so return to take a position on the long-standing and divergent framing of transfer in terms of either mental muscle or identical elements mechanisms.