Curving grades without creating competition among students
I think you're onto the right approach with the idea of a curve that only helps.
Based on your description, it sounds like you are in the United States. If so, the simplest way to do this would be to compute twice:
- Use the standard US metric of A=90%-100%, B=80-89%, C=70-79%, D=60-69%, F<60%.
- Apply the curve.
- Give the student the maximum of the two grades.
If you put together examinations that are far too difficult, then you may still have a problem. No matter what, however, a curve can only do so much to save you from this mistake, however, since overly difficult exams will also tend to increase the arbitrariness of assessment.
One other thing that may help in setting the curve is a trick I learned from the professor that I TAed for while in graduate school. When determining the curve, he also included all of the students who dropped the course. In a big undergraduate course, there were always a decent number of these, and they would generally be doing worse than the students who at least stuck it out to the end. The dropping student thus generally absorbed the failing grades at the bottom of the scale (except for a few deserving cases) and took the sting out of the curve for the students working hard but struggling in the class.
If a policy like this works to the detriment of an individual student, giving them a grade lower than what they fairly earned, then it is immoral. Such policies should be changed and the faculty should get together and come up with better policies.
However, interpreted in a certain way, there shouldn't be a problem, though, again, it takes buy in from faculty and administration. If the "half good - half bad" policy is interpreted as a goal to be achieved over time then it can be benign. If a course is offered in a term and the grades are "off" then the difficulty of the course should be adjusted for future offerings, with the already-earned grades standing as assigned.
Let me give two extreme cases. Suppose you wind up in a given term with a bunch of brilliant students. They are all overachievers and get near perfect marks on all graded work. How do you proceed? Flip coins?
The other extreme case, which I've actually seen happen, is that a group of students think they are overworked and "go on strike" and refuse to turn in any work at all. Again, how do you make this "curve" work? I was once the new faculty member who faced this situation when I worked a bunch of MS students harder than they were used to. I had to tell them that it was possible for everyone to fail in order to get them going again. I needed a discussion with the Dean to justify this, but she agreed and it worked out. The students got to work and raised their standards.
The grading scheme needs to be fair on its face to every individual. They should have a good idea along the way how they will likely come out at the end and what they still need to do to achieve their personal goal in the course. If the grading scheme doesn't do that then it is immoral and needs to be fixed. Student life shouldn't be a battle against unfair odds.
I find your instincts here to be good and appropriate.
However, if your class grades deviate from the norm, be prepared to answer why. You need to justify your actions, of course, and you may need to adjust the student tasks to make a desired overall outcome more likely. But a rigid scheme will eventually be unfair to someone.
"Fix" the policy, not the (individual) grades. Adjust the difficulty of the course over time to match expectations.
Let me add a couple of notes for balance.
A department wide grading scheme that leaves all courses of "approximately" the same difficulty can actually serve students well. If the standards are high, then students, when they join a course, know how hard they are expected to work and that it will be pretty hard. It also prevents some "gaming" by students who seek an easy path by choosing courses or professors. There is no problem with this until it is misapplied to a single section/course/professor.
When it is applied to the course of a new professor, without thought or understanding, it is also unfair to that person who may need some time to become adjusted to the students and their expectations.
Finally, I'll note that it sometimes becomes necessary to provide a "gate" to a major as the university may not have the resources to handle a too-large number of advanced students. CS sometimes has to deal with this when the field becomes "hot" for some external reason, driving too many students to want to major in it. These gates can take many forms, such as not being able to declare the major until the end of the second year and requiring certain grades in foundation courses to do so. This is necessary, if unfortunate. But the system still needs to be fair to individuals and not contain hidden traps.
Achieve the grade targets through iterations of the class across multiple semesters, not by curving the marks.
Simply put, your goal is to produce a particular shape to the marks without treating students unfairly. So, simply teach the course, and assess it at a level of difficulty you think is appropriate.
Then, if you're off your desired grade distribution after the semester's over, you know how to adjust it the next time you're teaching. If too many students get high grades, you can increase the difficulty of the assessment next semester. If too many students get low marks, you can decrease the difficulty next semester.
This process can be repeated until your grade distribution is at about the level desired by the university. If one of the other professors criticizes you for being off the desired mark threshold, simply tell them that you're new and you're still in the process of calibrating the difficulty of the course. It's an iterative process, and you're probably not going to get it right the first time.