I realize our education system teaches students that each subject is departmentalized, but it's been a real pain in the arse convincing students that completing the minimum sentence or length requirement does not necessarily constitute a good performance. I'm bombarded with questions about why they should write in a science class.
I have developed a new system that so far has worked spectacularly: I specify a minimal length (10-16) sentences but it is all contingent on the standard deviation for the class. You won't fail length requirements with 10 sentences, but if it's outside the standard deviation you're not getting anything else. Sometimes if people write above the standard deviation AND the rest of their rubric is a passing grade, I'll provide bonus points. Most of the time the first range exists slightly above the mean. In the aforementioned 10-16 sentence paper, I would have received about an average of 11 hours compared to now where I'd typically find 14.