Only extracurricularly - summer programs etc. Those were generally good, but not comparable in my mind since all the kids there wanted to be there, as opposed to schools (especially public schools) having a dynamic befitting a jail.

There weren't enough "gifted" people around for the numbers to work out for #1. During my whole time, I was aware of one other student skipping a grade and only a handful taking classes from the next grade up. The closest I got in a school setting was one elective AP class in high school.

I only skipped two grades, going from older to average to younger. I could see a larger age gap being different for socialization, but not with regards to bullying - there is no gain from beating on someone that's much smaller.