I've got a pretty nice first PBL effort going here, thanks to basing it closely off of a model project I got from PBLU.org. However, I've got students who are freeloading off of others in their group. They are succumbing to what is a natural instinct for some young people: to see a learning environment that relies on teamwork as an opportunity for a mental vacation. The success story is that most of my students are highly engaged. It's pretty awesome. What can I do to help these others and not allow them to freeload? I'm hassling them now, and it is unpleasant for me. What is a strategy that can allow me to work smarter, not harder?