And I'll just add that I was that other sibling. My parents had no plan to have me assessed for GT until the evaluators asked if there were any other siblings, besides the two they had already tested. I think my parents' perceptions were quite skewed by the PG-ness of one of my siblings, and the eidetic memory and very strong personality of another. I was always happy and easy-going, and able to "pass" socially. I'm not 2e, but I simply didn't make as much noise, and I didn't look like their other GT kids.
I don't think not being tested then would have affected my development in language-related areas, which are better differentiated in general ed classrooms, anyway, or in science, because I grew up in a science-saturated household, but I think I probably would have coasted in math, as, at age 8, when I was identified, I was already internalizing the idea that I did not like/was not good at math because I found it not engaging (aka, boring). Children are amazingly quick at taking the blame for an instructional mismatch.
Curiously, I had previously been administered both the SB and the WPPSI as part of early entry to kindergarten, but my parents appear not to have had access to those results (other than, "yes, go ahead"), because they were surprised by the results of my testing.
Bottom line, though, I agree with Michelle. First, answer the question, "What would be the function of testing?"
