How to help reduce students' anxiety in an oral exam? Oral exams can have various pedagogical benefits in certain circumstances, but can also make some students feel anxious. After watching several students nervous-sweat their way through such an exam, I'm looking for ways to help them. 

How can an instructor help students relax and feel less nervous during an oral exam?
The following assorted suggestions stem from standard procedure at my department, which has a long-lasting experience with oral exams, and positive experiences reported by fellow students suffering from anxiety.


The exam begins with the student giving a brief elaboration of a topic of their choice (within the subject of the course). They can talk uninterrupted for a while, and then the exam gradually shifts to question-and-answer mode on this subtopic, probing whether the student actually understood what they are talking about. This has several advantages:


The student knows how the exam will begin and they can prepare the first few minutes. This avoids anxiety due to uncertainty.
The student is not dropped into interactive mode instantly, but gradually.
The student knows which topic will be examined first, they can prepare for this, which boosts confidence.
Not related to the question, it allows the examiner to estimate how well the student can structure the chosen topic (which usually goes hand in hand with understanding) and put it into the context of the course’s subject.

Do not ask questions that require long and elaborate answers, but go step-by-step, guiding the student if necessary, but only if necessary (so they have room to shine). For example, do not ask:


  Please tell me about [central result of course].


Instead ask a chain of questions, allowing the student to answer each of them, and adapt them depending on mistakes the student makes or similar. For example, the questions could be as follows:


  What does [central result of course] state?
  
  Why is it so important?
  
  Under which conditions does [central result] hold?
  
  Why is [some necessary condition] necessary?
  
  Why does [some sufficient condition] suffice for [central result]?


In a typical case, these questions are raising in difficulty with the first questions being something that every serious candidate should be able to answer without much thinking. This allows the student to get some confidence and get tuned to the topic before the questions become more difficult. Also, this avoids the impression of time pressure and the student knowing that they have to get to that bit which they are not confident about, even if they can score by explaining a lot of basics before that.
If you ask questions where the student shall apply their knowledge and which require some thinking time, do this after they succeeded with some simpler tasks and announce that this is a advanced task and that they have some time to think. This avoids fear of failure and gives an extra boost of confidence if they succeed.
Give positive feedback whenever you can. This does not mean that you should be drowning the student in praise, but rather avoid fuelling their anxieties by forgetting to let them know that they are correct when they are.
If the student makes a mistake in their elaborations, let the student finish first, assert what was correct and then remark or possibly ask about the mistake. For example, if the student is elaborating on some equation and made a sign flip, do not remark upon it right away, but let the student finish. Then praise what was correct and ask them to elaborate their reasoning for that sign again. This has the following advantages:


It doesn’t break the student’s flow by interrupting their elaborations and lowering their confidence due to the mistake.
It gives the student an opportunity to detect the mistake themselves, e.g., by detecting it due to a follow-up problem.

Announce the examination mode beforehand as much as reasonable, to reduce any uncertainty due to an unknown situation as far as possible.