grading group projects

[Jon Monroe]

Plant-ed;

I just finished teaching Plant Physiology (senior undergraduate level) and,
as always, I had them do a lengthy independent investigation in the lab.
Most groups had 3 students but one had 5.  In the past I gave each group
member the same grade (worth ~15% of the final grade) and let them work out
for themselves how to deal with group members that don't pull their weight.
This semester I had more complaints than usual, especially in the group of
5 (I won't make that mistake again!).  In the future I may want to try
using some form of evaluation in which some of the grade will be based on
effort.  How do others deal with this problem?  If you have a system that
works would you mind sharing it?

Thanks,

Jon

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