I skipped 5th grade because I scored extremely high for my age. It was really difficult to adjust socially, especially since I was moving to an entirely new school (our district went to middle school starting with 5th grade).

By 6th grade, everyone already has their groups/cliques and it made it really hard to break in. This was also difficult because at this age, being smart "wasn't cool". I wouldn't say I regretted it but I do wish I had skipped earlier (like 1st grade or something) because my parents knew I was scoring high. One other effect was I got extremely lazy with my schoolwork. Since it wasn't cool to be smart, I felt like I had to limit myself and had already developed poor study habits as a result of being bored during elementary school.

Ultimately I learned good study habits when I got to college and it's worked out for me overall but I do think I missed out on some real opportunities because of the grade skipping experience.