I think it really depends on your child. My DD took the Explore at age 9 (4th grade). The results were useful to me (not so much to the school, but that's another issue.) Given her personality, I'm glad we didn't have her take it in 3rd grade and almost wish we would have waited another year. She doesn't do well in pressure situations and dislikes tests.
DD was one of those kids who walked into and came out of the test in tears. She was emotionally exhausted. Not so much because she didn't know the answers, but because of the testing situation - it was a strange place with strange people and she gets really anxious before tests.
