Philip Sellew, "Composition of Didactic Scenes in Mark's Gospel," JBL 108 (1989): 613-634.

Sellew points out the narrative pattern of the teaching pericopae in Mark:

1) beginning with public instruction from Jesus,
which is followed by 2) a change of location,
in which 3) his close followers question him privately,
which gives rise to 4) a sarcastic retort from the Teacher,
and concluding with 5) a decisive explanation from Jesus.

Sellew concludes that these scenes were deliberately composed by Mark to illustrate successive stages in the relationship between disciples and Jesus.

Sellew's analysis is suggestive. It seems that there is much more to be done with this pattern than he spells out.