It's surprisingly difficult to reconcile work that engages every student's passions with work that leads to outcomes that are meaningful on a scale that goes beyond students and their families.
Here's what I mean by that: if students are doing a project that connects with what is meaningful to them personally, everyone will be doing their own project. I'm a big fan of this, and kids still work collaboratively when they do this, because they critique each other's work.
What this work lacks is scale - when everyone's doing their own thing, you can't so something like run a big science experiment. If you're doing meaningful, cutting-edge science, you need everyone working on what they're commissioned to work on. This means that you're going to be doing work that doesn't resonate with everybody - or rather, you might be able to find a piece of the project that resonates with everybody, but there will be a lot of work that people need to do that they don't find innately interesting. This applies equally to teacher-led and student-led projects: even if you are doing a large-scale science project that's student-driven, it will only work if it's driven by a few students, with everyone else getting on board to help realize their vision.
This means that you need to help individual students find their own “entry points” into a project that will make it meaningful to them.
There are moments (such as the project launch and the exhibition) where every student gets pumped up and joins in for pretty much the same reasons, and it feels good to be working as one big group. But full-group enthusiasm is ephemeral. It doesn't get you through a six-week project.
When you're talking about the project (as opposed to the project launch day), engagement is much more like trying to pass a bill through congress - every single person has their own particular interest that you need to appeal to. And the very fact that one group of people is excited about a project will be enough to make other people think "ehhh, this probably isn't my thing."
This isn't really surprising. Imagine going up to a group of fifty adults and saying "Hey, you all live in the same general vicinity, I'd like you all to work on a complex and important science experiment together, over the course of several months." It just wouldn't fly.
The extraordinary thing is the extent to which most students, most of the time, are ready to go out on a limb and give something a try, even it it's not the thing they would personally choose to do with their time.