For standardized tests, I've found that if I do enough practice tests, I can generally get a nearly perfect score, generally completing them in under the time limit.
The only exception for me was when I was practicing on the LSAT. I was only ever able to get a practice score of about 176 (out of 180) because I simply wasn't fast enough. And if I did it faster, my accuracy suffered.
I only have that problem with verbal standardized tests, not with science or math tests.
The only IQ test that I have laying around my house says that my IQ is 139 (when I was seven years old?).
Now, if you take my SAT score of 1440 (740/700), it says that I'm supposed to be at the 99.8th percentile using that comparison thingy. I wasn't really practicing for that one.
My GMAT score (770) puts me above 99.9th. I did enough practice tests to get an 800.
So, in my case, my standardized test scores were ending up above my tested IQ score.
I'm one data point, so you can take it for what's it's worth.
