We are free to grade our students in oral or written exams. Obviously, if only 1 or 2 students take the course, oral exams (~15-30 mins) are the way to go from an effort minimization perspective (no exam creation, room reservation, grading, post-exam inspection/review), as well as written exams for like 1000 students.

Can anyone provide experience on the effort/benefits of oral vs written exams? Is there a magic number of students where this changes?

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    Giving good, relevant oral exams is an art form in and of itself, which also has to factor in to the equation. – Jon Custer Jun 25 '19 at 17:14
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    Are you a professor or a TA? Tenured? – Buffy Jun 25 '19 at 17:35
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    If you think preparing a written exam is onerous, then double it for oral... and consider that you need a large number of questions because students talk to each other ! – Solar Mike Jun 25 '19 at 18:46
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    @FedericoPoloni, there is risk in oral exams unless you have a way to keep a record. If you are tenured you can weather accusations. Otherwise it can get sticky. – Buffy Jun 25 '19 at 18:58
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    You should also take into account the class you are teaching. For example, for a beginner math course, it is easy to get exam questions (just change the numbers in the matrix/function/etc. and you are good to go). On the other hand, for a really deep graduate level class, it might be hard to find exam questions that are both challenging and solvable in a few hours (and the few that exist might be well known or already in the textbook). – Dirk Jun 26 '19 at 5:05

There's really no universal answer, but it depends on the university regulations and on your willingness to listen to students for several hours.

To give a personal example, I've been running oral exams for about 20 years. My exams, which are for undergraduate students (2nd or 3rd year), typically consist of a written test (2-3 hours) plus an oral exam with a duration of about 30 min for the standard exam or 1 hour if the student prepares an optional part (e.g. the presentation of a scientific paper or a presentation on a lab work). If you fail the written test, you cannot take the oral exam. You can be failed also at the oral exam too.

For me, the critical factor is the distance between two exam sessions because, given the rules in my country, the students who failed in one session should be able to retake the exam in the next one. Typically, in my university, the distance between two exam sessions at the end of a course is of a couple of weeks.

So, in my case, the magic number is of about 100 students, 150 maximum. Of 100 students, typically about 70 students come to an exam session. Of these, about 50% fail the written test, which means that I remain with about 35 students for the oral exam. Assuming that 1/4 take the optional part, I need 9+26/2=22 hours for the oral exams, which can be done in one week, leaving some days for grading and for rescheduling students who can have unexpected issues (illness, other exams on the same day etc.).

The benefits of oral exams have been discussed at length in the answers to this question, and I really cannot overestimate their importance in learning. See also this related question.

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    Wow. Dedication. – Buffy Jun 25 '19 at 18:40
  • Agreed on the dedication. But also, wow, 50% failure rate? ;-) – Flyto Jun 25 '19 at 20:19
  • @Flyto Ha, but that's a low failure rate! In a distant past my bar was quite high and the failure rate was around 80%. Many years ago, after having passed the exam, a student told me: "I've finally passed this exam! This is the 22nd time that I tried it". My answer had been: "It's because you haven't studied the other 21 times" ;-) (regardless the appearances, no student was harmed in the process ;-) ) – Massimo Ortolano Jun 25 '19 at 20:32
  • Note also that such a high failure rate was not so uncommon in my country in the past for certain exams (some professors were eventually lifted from certain courses because they used to fail way too much and the backlog was unsustainable). – Massimo Ortolano Jun 25 '19 at 20:37
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    @Flyto The Italian system is a bit crazy. In my university, students have 6-7 attempts per year to take each exam separately. A student that takes a 50%-fail exam 6 times has a true failure rate of (50%)^6 = 1.6% (Yes, I know, this is poor statistics, but it gives you a rough idea). It's not clear to me who benefits from this system, but we are stuck with it because any attempt to reduce the number of retakes is fought with fierce opposition by the students. – Federico Poloni Jun 25 '19 at 22:06

My personal tipping point is about 30 students. Below that, oral exams are more efficient, above that, a written exam seems to be preferable for me.

Note that this depends a lot on other factors: where I am, there are teaching assistant that help proctoring and grading the exams, so written exams scale well to large sizes. However, we also have a "grade grubbing date" (exam inspection for the students) and this also takes some time. Also, our regulations state that we have oral exams of about 30-35 minutes for a lecture for which the written exam is about 180 minutes.

Regarding other points raised in comments and answers: Where I am we always need two people for an oral exam and one of them needs to write a protocol of the exam which is kept on file. Regarding the time for the preparation of the exam: I feel that preparing a well thought written exam takes a lot more time than doing an oral exam. For oral exams I usually design just a few core question and the rest of the exam flows around these questions. Sometimes I even make a few of these core question available to the students (and still some of them can't answer than properly...). Also, I find it pretty easy to adapt the questions slightly, if I have the feeling that the students know all my questions already.

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