I was going to say 2nd grade, only because it was a very conscious, clear as a bell memory (I could tell you where I was standing and the exact words that went through my head), a detached observation, moment of insight. In which the word "different" was key.

But -- though the memories are very clear, they were more a general "knowing" than a moment where the world stops. That would be kindergarten and first grade. I didn't talk. In school anyway, because of being exceedingly shy and not being able to relate to others. I would give a tap on my kindergarten teacher to hand something in. Never a word. In first grade, they put me in the "slow" (this was a long time ago) reading group, interpreting quietness as not knowing/understanding. Except that I totally did. Reading. Pffft. No biggie. They didn't realize I was writing in (self-taught) script before kindergarten and couldn't believe it wasn't taught until 2nd grade(!) Anyway, ha, yeah, when I actually did speak, at the first lesson, they moved me up to the other group immediately. Lol. But socially, I was very awkward. It was a whole different story on that front.

It was kind of like being from another planet, but it's more accurate to say that I was in my own world.(Uhhh, and remain so to this day. ) It's funny to think... every available opportunity in first grade I spent whirling around in the Sit and Spin (Do they still have those? Probably not.) So... even had a literal orbit! Haha.

(Now of course trying to find a pic online and "no no no, that's not what it looked like!" Maybe it had a different name. Will research more. )