There is a critical bug in the way how Workshop pre-2.0 calculates the grading grade. Imagine the following grades given by peers (out of 100): 40, 40, 80, 80. The expected behaviour is that Workshop can't calculate the grading grade automatically and has to ask teacher for her assessment. What actually happens is that Workshop chooses "40" as the best grade (giving 100%) to it and then it considers "80" as a wrong assessment (giving 60% to it).
Reason: the best grade calculation does not expect more than one peaks in the grading histogram and stops at the first peak. See lib.php::workshop_grade_assessments()

Solution: fix the bug, then think more about the algorithm, eventually propose completely different approach