I never took a CWI class however attended various welding schools and became interested in reading about welding as much as doing it. The self study thing worked for me. I know a couple of guys here in my area that I think would do fine on some self study but they are gonna take the class anyway.
In my opinion
1) You need to know how to use the code.
2) You need to have a very good understanding of welding terms and definitions. Learning these definitions makes learning related topics easier.
3) The AWS Welding Handbook Volume 1 has most if not all of the subject matter on the CWI exam. If you like to just casually pick up a book and read. Thats one to have. I have used it for all three times I have tested by just opening up every once in awhile and randomly picking an area to read.
4) Practice reading questions. Any kind of questions.
If you have on hands experience using the code you should have no problem. On my 2nd exam (Let it lapse after 9) I was informed that the code I was taking was D1.1 instead of B31.1/Sec IX. I never "Studied" that code but used it in my job as QC Manager. I probably did better because I paid closer attention to looking up the answers.
I have thought about making an online survey on my website to gather peoples information about their CWI testing experience and results. I think we could get some interesting information.
Have a nice day
Gerald Austin
http://weldingdata.com/