In reality, it's probably not that much different from teaching the Core Plus Math Project CPMP) all those years ago or using rich problems and situations to teach a concept (those are about 2 or 3 days). There is a difference though. Inquiry from a situation still has quite a bit of built-in scaffolding and classroom conversations to formalize the content; I still have control. Maybe that's the reason project-based learning is so scary to me--I have to let go and trust the students to stay on task and learn what they need to learn.
This summer, several of us from #MichEd are trying to develop PBL lessons together at MichEdMath.weebly.com. We'll see how it goes.