denio...I taught AWS CWI review courses early in the development of the CWI designation. I found that many knowledgeable individuals failed the exam because they were not used to taking exams. In my courses I taught the technical provisions as well at "how to take the exam". I did not "teach the exam", but I did teach some test taking strategies. At that time, there were three code choices...AWS, API and ASME....you'd have to be nuts to choose ASME, even if you worked in it. AWS and API were much cleaner and more direct for examination purposes...the exam has changed though, so I'm not familiar with the current code selection.
In any case, be prepared for the test format and timing. That's important. As connectegr noted, PE's have failed the test, as have those with tremendous welding experience.