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.