My experience may not be typical, but it speaks to a couple of the questions posters have brought up.
We moved from Massachusetts to Missisippi between 1st and 2nd grades. I don’t remember any real problems with educational issues, but the social ones - oh, my…
This was the mid 60’s and the school I went to had just been desegregated the year before. To say there were stilll some major adjustments going on would be an understatement. And as “the Yank”, I was more than a little bit suspect. It was very much three years of a “Stranger in a strange land” experience for me.
We moved from Mississippi to Great Britain after the 4th grade, then back to the U.S. when I became a sophomore in High School.
Going to England, due to the deal my Dad got from his employer, I was enrolled in good schools, what we in the States would call Prep schools, but were called Public Schools in England.
Going in, I found the English schools to be much more demanding. I was put in with my age cohort, who had already been studying French and Latin for a couple of years. While I worked hard to catch up, I never did, especially in Latin. Eventually, I was allowed to quit Latin and substitute some extra mathematics. But I took French all five years, never getting good grades, but learning a lot.
I also studied History and Geography from an English perspective, which is not the same as a U.S. perspective. To this day, I know more about William the Conqueror and his descendants than I do some periods in U.S. History.
After a couple of years, at a new school, I started studying all the sciences - Biology, Chemistry and Physics. So I had three years of each of these.
When we came back to the States, my HS guidance counselor looked at my transcript and decided my 3 years each of the sciences was equivalent to the 1 year of General Science that most HS Freshmen had taken. He further decided that since I didn’t get good grades in French, I wouldn’t get any credit for that.
Result - in French, I took three years, and got straight A’s without ever cracking a book. This infuriated my teacher, since she knew I was not applying myself. She repeatedly told me I was a bad example for my fellow students. I just told her “I already know this stuff. What do you want me to do, learn it again?”
In the sciences, I mostly coasted also, although there was some new material in physics, and I did get into an AP Biology class my senior year which covered some material new to me.
The down side to this was that, going into college, while I had the requisite knowledge, my study habits had atrophied, resulting in my having to develop them all over again.