The standardized conditions for administering the CogAT are to have just as much preparation as the test publisher provides, which is quite a lot, actually. (A psychologist I know points out that the SAT is quite a good general mental ability test precisely because all test-takers have the same opportunity to find full-length practice tests before taking the SAT for keeps.) For a LOT more about the background of how the CogAT was designed, see the test author's faculty webpage, with many documents free from the downloading.
http://faculty.education.uiowa.edu/david-lohman/home 
