Lave and Wenger's "Situated Learning" (Cambridge University Press, 1991) includes 5 quite diverse studies of apprenticeship - Mexican midwives, Liberian tailors, US navy quartermasters, butchers and members of Alcoholics Anonymous.
"In all five cases described in the preceding chapter researchers insist that there is very little observable teaching; the more basic phenomenon is learning. The practice of the community creates the potential "curriculum" in the broadest sense - that which may be learned by newcomers with legitimate peripheral access.
Learning activity appears to have a characteristic pattern. There are strong goals for learning because learners, as peripheral participants, can develop a view of what the whole enterprise is about, and what there is to be learned. Learning itself is an improvised practice: A learning curriculum unfolds in opportunities for engagement in practice. It is not specified as a set of dictates for proper practice. In apprenticeship opportunities for learning are, more often than not, given structure by work practices instead of by strongly assymetrical master-apprentice relations."
As I read this stuff, my brain is running both training for ministry and equipping for discipleship through the authors' lens. In terms of discipleship, it seems to me here that 'strong goals for learning' and 'engagement in practice' are key dimensions - in other words, purposeful participation. When I consider ministry students, learning as improvised practice seems critical. The relationship with a mentor or supervisor is less critical than is the opportunity (and responsibility) of 'playful' and experimental involvement in aspects of leadership.
There is so much other good stuff in this book. I skimmed it a few years ago and am now re-reading it properly.