Maryann Aita, Writer, expert tutor, and creative writing MFA candidate
Rubrics and standards are valuable tools for grading papers objectively, but I would add that students can be graded on their effort to incorporate elements discussed in class as well. As a creative writing teacher, I provide rubrics and grade on how much students tried to use the stylistic elements or concepts we talk about in our lessons.
For instance, in doing a class with fifth graders on how to "show" instead of "tell," I spent the class discussing things like using verbs instead of adjectives and had the students come up with examples (like "He galloped across the room" instead of "he walked quickly across the room") and various examples of figurative language. Then, I can give higher grades based on whether or not the student tried using any of these elements. Even if they don't have talent as a writer (or visual artist or other very subjective form), they have materials to work with. Instead of grading on how much I liked the story or the literary merit of it, I grade on whether or not they made an attempt to apply what they learned in class.
The same goes for academic writing. Teachers should cover how to make an argument, what a topic sentence is, and how to present evidence. There is always some subjectivity in determining how well a student argued a point, but it is fairly simple to determine whether or not a student followed the guidelines of the assignment and tried to incorporate the principles they learned.