For many, it's the most stressful part of the job -- partly because it's so hard to be fair.

Despite what many outsiders may think of teachers and their work lives, it's a demanding occupation. My wife and I received a Christmas card from a former colleague of hers, an accomplished woman who previously had a successful career in economic analysis of energy issues and who recently had become a high-school teacher. She wrote that it is "the hardest job" she's ever had -- also the most satisfying.

I didn't have difficulty understanding either part of her assessment. But as I thought about her and her new job, I found myself thinking more about what's hard about it. For one thing, this person is still in her first year of teaching, which is notoriously demanding. I don't believe I ever worked harder or longer hours than I did in my first year of teaching high school -- and that includes my graduate school years and my first years of teaching at the college level.

After that first or second year, the workload becomes more manageable, but the hardest -- and, to me, most stressful and distressing -- part of the job remains: grading students' work. It's the part of the job that, in my opinion, induces the greatest uncertainty, discomfort, and angst.

An essay that earns a B+ at one moment might earn a B- the next day. It shouldn't be that way, but any honest teacher will admit it's true.

I know that some teachers actually enjoy grading. They say they find it interesting to see what their students have learned and how they're doing. I admire that attitude. And it's certainly true that there is the positive feeling that comes from the occasional observation of student improvement, from either increased effort or better understanding of the material. But apart from that, I was never able to get myself into the frame of mind where I could find grading bearable, much less enjoy it. Why not? Multiple factors and worries contributed to the pain:

The sheer drudgery and tedium. When you're two-thirds of the way through 35 essays on why the Supreme Court's decision in the case of McCulloch v. Maryland is important for an understanding of the development of American federalism, it takes a strong spirit not to want to poke your eyes out with a steak knife rather than read one more. I have lots of friends who are teachers and professors. Their tweets and Facebook status updates when they're in the midst of grading provide glimpses into minds on the edge of the abyss -- and, in some cases, already deranged.

Concerns about whether our tests gauge what students know. As teachers, we think we're clear about signaling to our students what we want them to pay special attention to -- what facts, concepts, frameworks they should focus on in their studying. But none of us communicates perfectly. When we pose an essay question about, say, McCulloch v. Maryland, are we being unfair to the student who can't say anything meaningful about that case but can tell us everything worth knowing (and more) about the decision five years later in Gibbons v. Ogden?

Concerns about whether we're testing what's worth knowing. Maybe that kid's right -- the one in the back row who says, "Why do we need to know any of this detail? Who cares about Supreme Court cases from 200 years ago? Isn't it enough to understand the contemporary state of American federalism? And maybe get that the conflicts underpinning these cases continue today?" Maybe so. Just because I'm a teacher doesn't make me infallible as a sifter and sorter of "important" information.

Concerns about what to weigh in making judgments. Every teacher has had the experience of handing back to a student a piece of work that merited a lower grade than the student was expecting and getting the comment, freighted with frustration and disappointment, "But I worked so hard on this." Probably so. But isn't the product of the work, not the effort itself, what the teacher must judge? I think so. But does that mean effort counts for nothing? And what about a science teacher who agonizes about whether she should consider grammar and syntax when grading lab reports?

Concerns about equity and fairness. No matter how hard you try, you realize there's a good chance you're grading some students more harshly than they deserve, and giving others more credit than they deserve. This doesn't have anything to do with favoritism (a whole other problem), but with human error and weakness. Your temperament and disposition change over the hours or days you spend grading an assignment. In fact, your frame of mind can change in moments for any number of reasons: Five weak essays in a row can put you in a foul mood; fatigue can set in; a too-hot or too-noisy room can set your nerves on edge. Maybe you're suddenly reminded that you have only 48 hours left to finish clearing out your deceased parent's apartment. How can any teacher be confident that his or her assessment of student work is always fair and accurate in the face of such vagaries? An essay that earns a B+ at one moment might earn a B- the next day. It shouldn't be that way, but any honest teacher will admit it's true.

Concerns about comparability of our evaluations. How do my judgments about this essay or term paper -- or of this student over the course of a semester -- compare with the judgments one of my colleagues down the hall would make of the same work? That is, there are even larger concerns about equity when the same student who earns a B from me would get a C in Ms. Smith's class or an A in Mr. Brown's. That same concern gets magnified, of course, when one broadens the field of vision to include whole school districts, states, or the nation as a whole.

Some people may find in this last point the basis for an argument in favor of statewide (or nationwide) standardized tests. I do not. I believe mandatory testing of that sort has been harmful to American education, but that's a topic I'll take up on another occasion.

Anyone who's taught for a number of years could add to this litany of woes. So could I. In any case, these are some of the worries that combine to make grading students' work a singularly unpleasant and stressful task -- for me, at least.

Having retired from teaching last June, I've graded my last test, plowed through my last set of essays, read my last term paper. I wish I could impart to colleagues still in the trenches some wisdom about how to make grading less agonizing. Alas, I don't know how to solve most of the core dilemmas outlined above. But with respect to one -- the drudgery and tedium associated with grading -- there are, of course, time-tested methods that teachers have been using for years. (Here are a few to consider.) Alcohol also helps, but exacerbates some of the concerns above. In any case, whatever else you do, lock away those steak knives.