- expected worst case is 20% penalty.
- Your containing category (assumed the course grade category) set to Weighted Mean of Grades agg method
- this item contained in it being worth 20%
- Subcategory of course category worth 80%
- Everyone starts out with perfect score for penalty item until they start missing class too much
If you can determine the relative "worst case" you could create a grade item with a weight of the "worst case" and award everyone the maximum until they suffer the consequences. Example: