I only have one in mind, DS' Kindergarden teacher in Montessori school he went to, who is also teaching my DS4.5.
She never said a word of "Gifted" about DS7 but mentioned casually to me that DS will be smartest in his first grade class.
Now we are having major motivational issues with DS4.5, as he does not want to do anything and constantly spacing out in the classroom, especially with a younger teacher who is pretty strict. He refused to do anything with her. DS4.5 is the one we don't think is nearly as smart. We nearly pulled him out of Montessori last year as he was just wasting time there and not making friends at all. We were going to put him in a traditional preschool where it's "fun" activity all day long.
Of course, like everything I do, it takes me forever to take an action. I have not transferred him so far. I am still not sure if it's good or not.
