Hoagies has some information on the different types of test. Good place to start.

http://www.hoagiesgifted.org/tests_tell_us.htm

My ds now 13 took the OLSAT a few times in elementary and was all over the board with respect to results. He said he hated the test, it was stupid (not sure what he meant). I think 3rd grade was his last time taking it.

Others will be along with much more information.