Not to scare you, but there were a few children coming out of the testing room in tears when my dd took the Explore last year. It is a real concern. Would he be upset if he didn't know how to answer several (maybe even many) questions?
Just to provide the perspective of a parent who had one of those crying children
... Dd13 took the EXPLORE when she was a year older than your ds (a few months past her 9th bd/4th grade). She didn't do her best, timed things are not good for her b/c her processing speed is slow, and she came out crying. She didn't finish parts of it and, in some areas like reading where she left the test repeatedly to go to the bathroom b/c she was crying, I really don't think that it was her best showing.
However, it overall turned out to be a good thing for her. She was bogged down with some significant perfectionism at the time and that, combined with a grade skip the next year, helped her learn to deal better with things that weren't cake walks. She took the EXPLORE as part of a consideration of a grade skip. If she had been homeschooling at that time and the purpose was to get a baseline achievement score, I don't know that this would have been the test I would have chosen, though.
Essentially I'm saying that I don't know if it would be the test I'd pick in your situation but that it isn't always a terrible thing even when the child is overwhelmed by it if you do wind up having him take it.
