@wetb4igetinthewater , you mention two different situations where instructor candidates perform skills during the instructor examination:
1) Performing skill demos thereby proving that they are able to demonstrate skills to students.
2) Posing as students for other instructor candidates who then have to make sure that they fulfil the performance requirements for the skill.
Let's say during my IE, one of the "students" is to perform the scuba kit removal and replacement at the surface. They are assigned the problem of not having a snorkel or regulator in their mouth. Because of the way I was trained, I don't catch that.
You do see the issue here right? Please tell me you do, as I think this is insane. Absolutely insane.
How can a training organization list a set of problems and allow instructors to demo those problems?!?!?
I think what you are talking about is situation 2, instructor candidates posing as students. I will call those "fake students" in the following.
In this situation, the "fake student" will be assigned some mistake to make during the performance of the skill. The instructor of the fake student must then do 2 things:
a) Not approve a skill performance unless the performance requirements are met
b) Help guide the student to perform the skill in a manner fulfilling the performance requirements
The guide to teaching contains a list of "Commonly encountered problems" which I believe you are referring to. Note that this is not a list of "errors" but a list of "problems". This list is there to assist with point (b).
Let's take partially flooded mask clearing as an example. The performance requirement in Confined Water dive 1 is "Clear a partially flooded mask.". No more, no less. If the fake student fails to do that, then the instructor needs to identify what the problem is. The list of commonly encountered problems can help with that. That is what that list is for - it is a troubleshooting list, not a list of requirements. It is also not a complete list of problems that can cause a student to fail to meet a performance requirement. There could be other reasons why a student fails to clear his mask than the common problems listed.
I hope this helps to clarify the difference between "Commonly encountered problems" and "Performance requirements".
Maybe some confusion is caused by the fact that there is a lot of overlap between the points in the "Commonly encountered problems" and the "Performance requirements". Let's take an example: the hovering skill from Confined Water dive 3. The performance requirement is
"Hover using buoyancy control for at least 30 seconds, without kicking or sculling." In the list of commonly encountered problems one of the points is
"Using hands/legs to maintain position — sculling". Since this "problem" is also a direct failure to meet the performance requirement, it is required of an instructor candidate to identify and correct it if a "fake student" does it. But some of the commonly encountered problems do not
necessarily result in a failure to meet the performance requirement and in that case they do not necessarily need to be corrected.
As an instructor candidate you are being tested in your ability to detect and correct
any problem that causes a student to fail to meet the performance requirement for a skill. Not only those problems listed in the Commonly encountered problems list. That list is just a helpful guide.