Tim:
We encountered the same problem with our TBL course (120 students). We then instituted a policy that students must achieve 70% average on individual exams for the group work grades to factor into the final grade.
Unlikely, I know, but what happens if the group work grades are worse than the individual grades? Does the student have a choice about accepting the "weight" of the group on his or her final grade? Tim seemed concerned that an individual not benefit unduly from a group's success? Does the same hold true if the group doesn't perform well?
Now, if a student does not achieve a 70% average on exams, then the group scores do not factor in, and the course grade is based only on the individual exam scores.
Assuming students see this policy on the syllabus at the start of the semester, might they see this as TBL "escape clause," and decide not to commit themselves to the group up front if they feel they can get out of it on the back end.
Ed: Don't get me wrong: I like the policy. Just playing devil's advocate a bit.
Thx,
John
Asst. VP, Instructional Technology & New Media