Turning the flywheel

I've been reading How the Mighty Fall by Jim Collins. If you haven't gotten to them, Good to Great and Built to Last are also excellent reads if you're interested in organization building.In the appendix he restates the principles from Good to Great. The one that really got me thinking was The Flywheel. Quote:

There is no single defining action, no grand program, no one killer innovation, no solitary lucky break, no miracle moment. Rather, the process resembles relentlessly pushing a giant heavy flywheel, turn upon turn, building momentum until a point of breakthrough, and beyond. (182)

So how do we get the flywheel turning on changing assessment practices? How do we build that critical momentum to reach that breakthrough point? I've been taking the one-teacher-at-a-time approach but frankly, it's slow. On the surface it seems like I'm making progress. It was a team of 1 last year and now we're up to 8 teachers trying things out. The problem is I'm converting those that want to be converted. The low hanging fruit. How do we reach a point where even those that resist all change are swept up and brought along?