A modulars ago, I assigned group projects to students. Everyone worked well together except one group. There were two slackers. Ironically, these two slackers had the same issue with another instructor prior to coming to my class but yet, they chose to work together again.
One the day when the project was due, I had each person from each group grade their fellow classmates. To my surprise, they were all fare. As for the slackers, first student did not come to school. that student received a zero. The second student, stayed in the LRC all class section to make up project. The second student not only was marked absent, also got 60% for the project. It was late, unorganized, errors and so forth.
As a result, I decided to use this individual assessment form for group projects. It works well and the feedback is great.