DD9 is just starting to grow out of this behavior. A lot of it stems from her literalness - if someone asks what grade she's in, she has to specify "3rd grade Prism" (which is always heard as "3rd grade prison" and then we go down a different conversational path). She can't seem to bring herself to just say "3rd grade." Actually, the last time someone asked, she said "3rd grade gifted," and I told her afterward that that was much better. I've explained that when people ask that, they are usually trying to ask "how old are you?" but to be more polite about it, so she doesn't have to quantify that she's doing 4th grade curriculum in 3rd grade, but it's still hard for her to grasp.
DS4 doesn't really carry on coherent conversations yet, so it hasn't been a huge deal with him. (He converses with interest, but he's sort of all over the place, so you're never 100% sure whether he's answering you or just saying something that popped into his mind.) We'll cross that bridge when we come to it.
