DS tested in 3rd after a grade skip, so he was 7 1/2. It wasn't a big deal... If it had been anxiety-provoking we wouldn't have done it, but it didn't bother him at all. He knew he wouldn't finish and that it was meant to be hard, and although he was definitely tired afterwards he wasn't shellshocked or anything.
We did Explore rather than the SCAT because at that age two a year might have been more than he wanted... and because the Explore was acceptable as an annual test for homeschoolers. (NC requires annual testing.) We did it again at 8 1/2 and at 9 1/2 (that was last year) and then switched to the ACT.
I agree with Dottie's list - in our case #1 was the biggie just because he was extra-young. And last year with the ACT it was the biggie again (ACT is more like 5 hours). I think also the
parent should be prepared for low scores -- DS's first Explore scores were much lower than subsequent ones, and his first ACT was slightly lower than I expected... with a definite down-trend as he got tired.
