This point is already part-argued: play’s close links to innovation – and the fact that, as quoted in that post, the drive to play arises from its nature as “training for the unexpected” – make its equally close links to learning obvious. (I’m making this point briefly, but it’s a crucially important one.)
Then there’s the clear implications of the well-known “10,000 hours theory” – the idea that excellence in any field is achieved in large part by spending 10,000 hours doing it with constant feedback. Play implies a degree of interaction with and varying response to the outcomes of the various objects of play and actions being tried; it isn’t play if it’s monotonous repetition! It also motivates this kind of persistence in a task.
But, again, common sense tells us that play is a powerful tool for learning. The old adage “show, don’t tell” is true as far as it goes, and not all lessons can be learned hands-on (at least without a degree of preparation… and in some cases, warning!), but for learning how to actually do something, for any actual application of information to real-world conduct, and even in many cases for a better understanding of abstract properties, “play with” will always trump “look at”.
This is why young children are such sensovores: they are trying to learn all the different qualities of things (including, of course, their own bodies and senses). They play with things by looking, listening, feeling, smelling and tasting – and shaking, throwing, hitting and otherwise manipulating with all the precision they can muster while they are still just starting to learn precision. Given that very few people have conscious memories of life at this age, and even if they did these memories would almost certainly be sense-memories not informed by conscious strategic/analytic/symbolic thought, it’s harder for us now as socialised and enculturated beings to recall the pressing experimental drive that underpins this profound encounter with reality on its own terms, but given what we know of brain development at the ages where play is most prevalent (I could say “unadulterated”) it seems safe to say that the smartest period of our lives – not the most knowledgeable, but the smartest, the time when we work the most stuff out the fastest – is the most playful.
There are also the fascinating parallels between the psychological state of “flow” – discussed in this post; what Csiksentmihalyi calls “optimal experience”, but is often (though not always) experienced as transcendent fun – and the needs of learning. Indeed, if you look at the way that flow is defined – roughly, staying in a zone where you are challenged but not overwhelmed as you improve your skill in the action you are undertaking – and compare that to educational theories around presenting students with material that will keep them stretching to learn (I’m thinking here of Vygotsky’s “zone of proximal development” and the notion of “scaffolding”) the links between play and learning become even more apparent.
Even setting aside these considerations, the most rote and informational of learning (which on first glance would seem not to lend itself to play) benefits from external incentives – and not just gamification-style motivational incentives, though those can certainly work, but concrete external links onto which to scaffold the learning and ground it into the real. The basics of logic or mathematics or system dynamics or the laws of physics make far more sense to those still learning them if manifested in a form that students can manipulate to experience the interactions for themselves. Yes, at some point they need to stop playing with the props and start playing in their imaginations if they are going to develop new understandings of their material, especially the more complex or counterintuitive parts. But it’s impossible to deny that play is a highly effective hack for uploading those abstract principles (at escalating levels of abstraction) into a brain designed first and foremost to engage with the concrete physical world… and playfulness doesn’t stop being a useful tool once those less-evident truths have been so uploaded.