We have used the released questions from the California Achievement Test, but more as a teaching tool. I started ds at his age/grade level and used it to show him how to answer multi-choice questions as we has done very little of those (I would rather find out what he knows from narration).
We didn't do it as one big test, but just did about 15 minutes each day and talked about how to eliminate obviously wrong answers etc. He was enjoying it so we continued and went up the next several grade levels until we got to the point that there was lots of stuff he didn't know.
That information was interesting for me, to see what level he was working at, but didn't mean anything to ds as he didn't know what the 5,6 or 7 referred to (he's always confused when people ask him what grade he is in - it is just not something that is relevant to us).
We have not been required to do any testing in any of the countries we have lived in (so far), but at some point he will probably have to do some form of standardised tests so I wanted him to at least be familiar with them (even if I don't see much value in them).