May academic credit be withheld as punishment under a good conduct policy?
No.
The withholding of academic credit as punishment for non-academic misconduct is disfavored. Courts have considered grade reductions an unwarranted extra punishment and an improper technique whereby a school makes a clear misrepresentation of the student's scholastic achievement. In re Nielsen. Nelson & Burns. 13 D.o.E. App. Dec. 284 (1996).