this is about a phenomenon often seen, but I came across a probably more prominent example recently, so I thought I'd ask for the community's opinion.
Here's the situation: In the past semester's exams there was a question in computer architecture asking for X, and I, and many other students, answered Y, which contains X and is mostly revolving around X, thus successfully answering the question (in our opinion at least). The professor rejected the entire question (20% of the grade) and at any attempt to talk to him he directed us to the sample answer, stating that we "are wrong", we "answered another question, not the one asked", and so on. The question wasn't even given partial credit, and that happens systematically in his tests.
Another similar issue on the same test, was when a very few of us optimized a small bit of code in a way that would, industrially, be significant, and that part was rejected similarly, without any explanations, as "being entirely different". Explanations were also written on the test, so he cannot claim we did it without explaining.
This seems to be a general policy of the professor, as numerical errors are similarly crippling to grades, and in the sequel lesson, of an amphitheater of about or more than 80 people (and of course a lot more don't even attend classes as they are not obligatory, but I don't know if they're better or worse than those who attend), only 11 had succeeded the exam.
I would finally like to note that some of the stuff he rejects, he himself does in class, the most obvious being a computational error, and frustratingly he also did the optimization he rejected in the test.
So finally, the question:
I understand that professors have the right to grade based on their own criteria, but
Is it justifiable to reject an entire answer because more was said, without even partial credit?
Is it justifiable to reject an answer that gives something better than what is required, perfectly equivalent, even if relying on the student's intervention? (in this case, it would be a compiler optimization, thus not an entirely direct interpretation, but an elegant and industrially valuable workaround)
Is it acceptable to direct students to example answers and not allow them to explain why they think their answer is correct?
I'm also itching to see how we could deal with this, but that's not the main question so I leave that to your own discretion and benevolence to answer.