I endorse your closing thought that proleptic interactions should be a
two-way street. To take this a step further, however, I wonder how this
discussion of prolepsis might apply to more collaborative forms of
discourse in which none of the participants serve as the
teacher/master/expert. An example of such a conversation would be the
transcripts provided in Jeremy Roschelle's 1992 article in JLS ("Learning
by Collaboration: Convergent Conceptual Change") which involved two
students involved in a joint task to understand the behavior of a
ballistics simulation.
These conversations are proleptic in different way: the individual
utterances are ambiguous and incomplete, but presuppose that some form of
meaning will emerge in time. Instead of one party expecting the others to
accomodate, all parties participate in the construction of a shared
understanding. I would suspect that this more democratic version form of
prolepsis contributes to learning just as commonly as the scaffolding
version (at least outside of formal instructional settings). Certainly
this discussion group is proleptic in that way.
---Tim