Some of it could be that, Sue. I have seen many instances in which an exam candidate approaches a passing performance on a maneuver in a clinic, and gets that feedback, and then becomes disappointed when he or she does not pass that same maneuver on exam day. Some even get angry. "But my clinician said I was getting it," they insist. Hmm....
We must realize that approaching a particular level of performance in the nurturing environment of a clinic, with the coaching and guidance of a good clinician, is NOT the same as "owning" the skills! When you start to get it right under the watchful eye of a clinician, that is when learning BEGINS. It will take much practice to ingrain those movements and develop them to a level where you can apply them consistently, under pressure, in different circumstances, and with only your own kinesthetic feedback to guide you.
I've always said, "Learning BEGINS when you've got it right!"
Mock exams like those you describe are not uncommon, especially as "pretests" to determine whether or not to let instructors go to the real thing. As I've said, I think there are better ways, but you can get something out of virtually every skiing experience. I'm sure they aren't a waste of time, provided they don't just develop false expectations.