Hello! I'm going to pop in and share my experience (this applies to around Kindergarten to about fourth grade-ish)!
When I was younger (kinder-1st), I mostly got picked on for being small, weird and sensitive. Maybe it was because I said strange things, would do anything to talk about owls, or because I cried a lot. I was often called weird and left out of activities. I got laughed at since I'd always trip or drop things, when the reaction when someone else would was far less extreme.
As I moved into later grades (2nd-3rd) I stopped crying as much. I started trying to please a little more, by saying things I thought was funny- which actually got me some strange looks. Everything I did was something to be scrutinized, whether or not it was normal. I was called weird, again, a ton. I was called a "cat" (as an insult) because I pretended to be one with other bullied kids.
At the tail end of the bullying (4th-5th), I was still weird and small, but made sure no one thought I was sensitive. I'd pick fights a lot. so many rumors. so many "secrets". One went around where people weren't supposed to talk to me- I never found out why (rumors and secrets are super common with kids, by the way)
The bullying sort of dropped off and disappeared after that, but it certainly stuck with me, and still is stuck with me. People-pleasing, fake confidence (that quickly became fake arrogance), self-isolation and assuming the worst about what people thought of me became second nature.
Also, people always said to just tell a teacher. To keep it brief, that never worked. By then I felt like even the teachers didn't like me. They'd tell the person to stop but it only made things worse.
Luckily, this has definitely improved over the years and I'd say the "aftereffects" have begun to fade off, little by little, off and on. I hope this made sense and I hope this helps, and this is only my experience! if anything doesn't make sense or something feel free to ask :) good luck!