In my experience, who leads the session depends somewhat on the team and project. Usually, it’s led by the UX Lead (which really could be the same role as creative lead for some teams), though sometimes a product manager might lead. And yes, breaking into micro-groups definitely makes sense. One way to do that is to take an approach similar to the Pair Design model I propose in the following post.

Question as I didn’t see it explicitly mentioned, but do you see this session at least being lead by a creative lead (who may or may not be the visual designer)? Also I see value in breaking out into a microgroups (IA +VD) to broad stroke ideas and then present it for a group crit to dissect as per your above comments. Thoughts?
An agile implementation of your suggestions could even possibly include each thought area be taken as a separate iterative cycle (occurring a few times within a given week).

The reason I ask the above is that I’ve seen quite a bit proposed but in practice go a bit awry on the implementation side. Comments welcome. Good stuff all around though. – F

For example, once someone has presented an idea that it seems the team feels is strong, I might point out that the layout in their sketch is radically different from that of the legacy application and ask them to make a case for why the layout should change. Or if the layout appears to be completely non-standard, I might ask the developer to talk about how costly/complex it would be to implement. Or I might refer back to some research data that shows that the current user base has a wide range of monitor resolutions, and do we want to optimize for different layouts?

Fundamentally, I’ve found it to be less about education and more about team awareness that the grid is not something the visual designer should work on in isolation.