For testing, I just told my DS we needed to see what he's good at/what he's not so good at. His temperament is different from a lot of other kids -- he never hides who he is (probably his 2E causing this). He is usually eager to share information, so I did not share his test results with him (because of no/very little filter). He does know that he did well on most of them. His school does not have gifted ed. So, all he knows is, yes, he can learn things super easily. I think, for more socially-savvy gifted kids, it may not be such a loaded label.
With DS, who is younger, we've done the basic "Some people are good at drawing, or soccer, or singing...you've good at school things, like reading and math. You have a very speedy brain."
My kid has questioned why he is sometimes slow to complete worksheets, but has been able to easily fly through that exact same worksheet when asked verbally. I think some gifted kids are also motivated and driven, and school tends to be easy for such kids. For other kids, who have 2E issues, and are not as motivated by subject areas that they know already, school is challenging. His music teacher seems to think he is excellent -- he loves music theory (it puts me off to sleep). He also loves learning languages. But nothing bores him like mundane worksheets do
