Both of my DDs tested into our school district's GT program based on group administered tests (CoGat, NNAT). We paid for IQ and achievement testing with DD8 because we suspected (and confirmed) that she is twice exceptional. DD10 asked us why she had not been tested. I answered her honestly that she had not been having problems and seemed challenged by her current teachers. I assured her that we would pay for testing if we saw a need for it. She never brought it up again.
Recently, I've been trying to convince DD10 to take the Explore test through our local talent search. I have no hidden agenda. I'm just curious. DD10 replied that she is fine with school and doesn't want to give up a Saturday. At this age I can't see forcing her to take a test against her wishes. I guess one argument for testing at a younger age is that they may be more willing to take the test.