A reader in Columbus, Ohio, drew my attention to a story about a high school English teacher in Denton, Texas, who gave his students an assignment to write about a topic of their choice. One student wrote about a gun show. The teacher reportedly threatened to give the student a zero for the assignment, if he did not change his topic.

As the local Fox News affiliate reported, that student's mother expressed her disapproval with the teacher's response to her son's essay. The teacher maintained that he found the paper unacceptable because of his concerns about school violence. The mother maintained that her son's paper made no mention of firing guns, it simply reported on his gun show attendance.

Ultimately, the school district issued a statement to Fox News that read: "The teacher has accepted the paper and apologized to the student for misperceptions. The teacher's intent was for guns not to be trivialized in any school situation because of recent events."

My reader in Columbus wants to know if the teacher was right to threaten to give the student a zero.

"Does a teacher grade on content, style, or personal feelings?" my reader asks.

Say a teacher wants students to write about gay marriage, my reader continues. One student writes that he is opposed to gays getting married, while the teacher is in favor of gay marriage. "How should the student be graded? If the student did an excellent job in presenting his argument, should the teacher give him an A for composition, and an F because the student is wrong due to prejudice?"

Some challenging situations in the classroom can be avoided by intelligent construction of assignments. If the Texas teacher wanted to put parameters around what his students could and couldn't write about, then giving such a broadly worded assignment as writing on a topic of your choice was not particularly effective. Once the assignment was worded that way, it was only fair for the teacher to grade the essay based on its merits as an essay.

There was no indication that the student wrote about issues that presented a danger to classmates, teachers, staff or the school. The right thing would have been for the teacher to grade the essay based on the strength of the writing rather than on the topic.

The same goes for an essay on gay marriage. If a teacher asks students to write essays on gay marriage, he should be prepared for essays that might take a stance for or against the issue, regardless of his position. The grading should be based on how well the position was argued and how well the essay was written.

There are times when it's appropriate for students to be graded based on the stance they take on an issue. In school debates, students often draw lots to decide who will take which side of an argument. In such cases, it's perfectly reasonable to grade a student based on his stance, for example, on background checks for gun owners or the legalization of gay marriage.

But barring such circumstances, if an English teacher assigns an essay to gauge how a student can write, then the right thing is for him to either be specific about the assignment or to be prepared to entertain a whole swath of examples if he isn't. The teacher's focus should be on strengthening the students' thinking and writing, not on getting him to think like he does.

(Jeffrey L. Seglin, author of "The Right Thing: Conscience, Profit and Personal Responsibility in Today's Business," is a lecturer in public policy and director of the communications program at Harvard's Kennedy School. He is also the administrator of http://www.jeffreyseglin.com, a blog focused on ethical issues. Do you have ethical questions that you need answered? Send them to rightthing(at)comcast.net.)