I found a great posting on Edutopia.org today entitled 20 tips for project based learning. So many people are moving towards projects for learning but don't take the time to structure the project. Assigning a group project doesn't mean you can just throw out the assignment and hope it works. "Front loading" the lesson--structuring and planning ahead of time-- will result in much better results for you and your students!
These tips cover items like putting teams of students together for a long term--6-8 weeks. The same group could work together on several projects. Another good tip--make hetrogeneous groups and let the group play off each others' strengths.
The formative assessments are vital in projects! Students need to know as they are moving through the assignment how they are doing. I've always found more success when I have interim due dates for pieces of large projects--"Your idea list is due on this date." "Your draft is due on this date." Yes, it means more grading --but you get more grades! I tended to carry a clipboard and just make these "check" grades--you have it or you don't which equaled a 100 daily grade or a zero. It wasn't hard and was a good way for me to touch base with each group to check on progress.
In the library I see so many times teachers who assign projects so kids will work independently for a few days. Well, that's all well and good but doesn't mean it's time for a teacher to sit back and read the paper (and yes, that happens all too often.) Managing projects in a classroom is not different than managing projects in a small business--you need to know the status of each one at any given moment!
Take a look at the blog posting from Edutopia--what other tips would you add?