IQ test are pretty useless on the whole like you found out it varies according to the type of test you take. You're better of grabbing some of the old IQ tests that they used in the past and practice on them to get the score you desire for posting to the school you want. They aren't really any different from any other test that are covered in school so for some degree your score can be improve by practicing on simalar test. Its a case of knowing what type of questions you need to answer and then having experience in answering them.
Alex
