I didn't sign my DD up as a 3rd grader, but she was only 7, and I didn't think she'd be up for it. She's going to test this year as an 8yo 4th grader, but I'm mostly interested in getting a baseline for comparing future scores. (She did the SCAT a month or so ago, and did respectably but not outstandingly compared to other 4th graders. I anticipate she'll do respectably but not outstandingly compared to grademates on EXPLORE, too.)
I don't anticipate any issue with the getting up - the test location is relatively close to us, so we can leave the house just a bit earlier than we'd normally leave for school. But 4 hours is a long time - the SCAT was only an hour, and that totally wiped her. OTOH, most of the EXPLORE works with reading passages, and reading-related things are a strength for her, whereas analogies are not. On the gripping hand, that's a lot of manual bubbling in, and a lot of "I'm an anonymous tiny person in a room full of big people."
We do a breakfast treat and a burst of physical activity to get your brain going and your body settled down.
My big worry is that we'll have an ice storm or other weather making it hard to get there. The sites within reasonable driving distance for us are all February-only sites, so we can't reschedule if something comes up.
