Seriously, I came from Ukraine when I was 12 and being an out-of-shape immigrant and a nerd made my life in American school a living hell.
The problem I remember having the most was isolation. It's interesting because people did make fun of me in Ukraine all the time, but we made fun of everyone and were pretty much all friends, we conversed a lot, even when we were fighting.
In U.S. it's just different, people ignore you. Spending 8 hours in a place where no one talks to you except for teacher (and several accidental buddies) is pretty miserable. I often thought it'd be easier if I was bullied, at least someone would fucking notice me. Took me a around 4-5 years before I became a misantrophist and just started hating everyone by default and that's sort of how I managed living here.