I've not made much use of in-class exams before, but I gave the first one of this semester and it prompted the question in my mind of why do we give exams at all? Or, if we do give exams, why not simply give all the answers beforehand?
By reflex, we might respond that exams test learning. But do they? And if so, is the testing the sort of learning important for the students' future success -- rather than the ability to do well on exams?
A cynical response is that exams simply test the students' intellectual endowment, be it socio-economic (having gone to a good high school) or cognitive (of a certain type of intelligence). And we can't give everyone an A, and so we need some sort of filtering mechanism. I once heard this argument about the business school of an elite institution: it could be little more than a sieve selecting from quality students who then use the opportunity to network. What is actually taught in the two or three years there is inconsequential.
A reason I sense in my own motivation is to satisfy myself that the students are paying attention. That is, my choice of questions for the exam is a sample of all possible things the students ought to have learned. I had this experience as an undergraduate myself, especially in humanities-type courses. I went to class, paid attention, and I would know what was likely to be on the exam. Yet, to give exams so that students pay attention only so they do well on the exam is circular. When I was a student, I had a particularly poor calculus teacher to whom it made no sense to pay attention to. Instead, I took class time to study, do extra exercises, and visit the TA. I also had a wonderful statistics teacher who provided us with handouts to help us make sense of the material, upon which we were tested. I even had a computer science teacher who gave us a practice exam, and it turned out that it was also the in-class exam. (And I still know people have failed it!)
A more interesting reason is that the exam prompts students to study and prepare. So the exam itself isn't as important as the learning that one does in preparation. An even more interesting extension of this is that we use exams to teach students how to be good learners. That is, exams prompt students how to identify what's important, how to think critically, and to adopt tools for note-taking, mnemonics, etc. But how many teachers actually teach this?
There are many options, across varied disciplines, for giving exams: pop, planned, preceded by study questions, open notes, open book, or the take-home format. Does anyone know of a nice articulation of the types of exams and what types of learning they are intended to further?