Exams are an unrealistic way to judge ability. It would be incredibly rare for you to be in a work situation where you have the combination of; a short time to do something, not being allowed to speak, ask for help/guidance/info or check existing reference materials.

(I'm just adding an edit here: I understand that in jobs you're expected to know things, but that sort of knowledge more often than not - imo - will come with experience. In my current job, I know the answer to most questions fairly immediately, but if I'm required to, for example, write a formal response citing certain rules or regulations, I'm not expected to have memorised the text for these things, but have the facility to look them up. That's just a single example, of course. I appreciate that certain jobs - like paramedic, say - will require a great level of under-pressure knowledge, but again I would surmise that someone who has been doing the job for years but got a C in their final exam would likely have more aptitude than someone fresh out of school with 100% in the exam.

There's been a cracking debate as a result of this, though, and I've enjoyed reading all the points and counterpoints!)