We were lucky in that DS (then six) had participated in some research studies before his testing... mostly things for the audiology department at our local univ., so not really like the test itself, but the situations were similar: the person administering the test would have some specific things they could say and do and specific things they couldn't say or do because they had to make it all the same for everyone who took it or it wouldn't be good science. And I couldn't tell him anything about the stuff they'd ask because they had to only do the test with people who hadn't seen it before or it would mess up the results. Also he had to do his best because that's what they were testing for, but not to worry if he couldn't do everything because of course to find out everything he ~could~ do they couldn't stop until they got past that...
Apparently I played up the "can't tell what's on the test" part a little too much because he steadfastly refused to tell me any details afterwards because I had said no one can know until they take it! LOL
We never really discussed what it was for or anything, and I think he just assumed it was part of another study. It's been three years now and although he definitely remembers going, he never asks about it...