Not feeling comfortable could be question of time. You get comfortable when you go from kindergarten to 12th grade with the same kids. You know them well, because you've been in classes with a lot of them for 6-7 hours / day, 5 days a week, 9 months a year.
As I typed the above paragraph out, it actually makes me question. Is that really growing social skills if they're always surrounded by the same kids? For example, I moved to a different state between 8th grade and the start of high school. That experience helped me to understand what it's like to not have friends, how long it takes to make friends (2-3+ years), and how to interact with a lot of peers you don't know and who don't know you.
It was interesting when I went to college, and I found other students who were nice, but never really interested in being your friend because they went to the same college as many of their high school friends. Or they grew up near the college and had all their high school friends nearby still. I guess this latter point isn't really social skills, but it is something that I learned to be aware of.