DS did EXPLORE in 4th, very useful for him as he also needed to do ACT very early (6th grade) for advocacy reasons, and EXPLORE is formatted like the ACT. (I don't know if they're still offering it, there's been some waffling on that score, I believe.)
DS really enjoyed the experience of challenge he got from the test. It was also very useful to have a specific science score on him going forward-- so the school could see his needs more clearly. (We were hoping to get a useful math level too, but he hit the ceiling.) It was not useful right away, but a year later we needed that score and we were happy to have it in our pocket.
DS is a person who truly loves taking standardized tests. EXPLORE tested his stamina: it's four segments of about half an hour each. If he really didn't like testing, I probably wouldn't have gone this route.
