In terms of students and diversity, most people are friendly with oneanother, though there will always be groups or cliques: African Americans, multiethnic, Asian Americans, Eastern Europeans, Latin Americans, the athletes, the dancers, the trust-fund kids, the Orthodox Jews, the pre-med kids...there will always be groups people migrate in, but this is because they identify with oneanother, and thus spend time together. Its not exclusive, and people often have friends from all different groups. Thats what I love about Barnard; the diversity and the friendliness. You can be yourself and others will also embrace that, whatever you choose.
There are Barnard women from all over the country and the world. I have friends from the city(Staten Island, Brooklyn, the Bronx), New Jersey, California, Georgia, Indiana, Illinois, Maine, Tokyo, India, Spain, Miami, etc. Most of them come from more liberal areas, because it is a very left wing school. Students are very politically aware and active, and take part in rally's/protests...speak their minds to make change. Last semester, there was a racial incident on campus where a noose was hung on an African American teacher's door. There was alot of protest and rally from the college/university, as well as the surrounding neighborhood to let everyone know that intolerance and hate is not tolerated...thats pretty much the only thing that is not tolerated.
In terms of groups to join, there are so many. I am African American, so I attended a few BOSS(Black Organization of Soul Sisters)meetings. I was not an active member though, because my life primarily revolved around dance, both academically and extracurricularly. There is a student group for almost every racial, ethnic, religious, special interest group. There will be a niche for you, I promise. And if for some reason you feel that there is an area lacking, you can always start up your own group and get funding from the college. In terms of socio-economic status, there are people from all classes as well, because even though its expensive, there is alot of assistance given/financial aid.
I want to say that no one would feel out of place at Barnard. I think there is a place for everyone. Obviously though, if you didn't like the city, didn't want a small school, didn't want all girls(though thats not as big a deal as you would think) and didn't want a liberal, opinated environment full of diversity, where everyone is different and special, then you might feel a little out of place. But only a little, because you would quickly find out that Barnard is like no other, and would be fun years of trying something new.