Wow. You've given me a lot to think about and I think your analysis is dead on. I'll go you one better. Considering everything I'd have to say I now think my audience was not only American & white but also male and between the ages of 18 - 50 when I wrote it. I'm going to try to keep that in mind in the future. Thank you. I work for and with global audiences and have learned things like Celsius & metric conversion out of necessity (I still think in Fahrenheit & inches!) but when I'm writing technical papers I try to be very conscious of my international audience. I guess this did not translate to personal writings.
The answers to your questions reflect the state of the North East United States. I live in a moderately rural part of New England where there are many of these residential schools.
Our high-level demographics for the region are: Population: 140,000 - White 93%, Black 3%, Hispanic 4%
Back in the early 90s I believe the racial diversity of the region was even lower (ie: White 97%).
At the school, for the direct care workers whites were in the minority.
On the other hand our students came mostly from East coast cities (Baltimore (63% black), Washington (50% black), etc.) and were by the vast majority for families in poverty. In the 5 years I worked there we had only one "rich" kid (he was white) who had been expelled from private school and arrested for arson after he set another student's bike on fire. I remember that his grandfather was a state senator. He was also the only kid who's tuition was not paid by his home state. The rest of the kids had been arrested, expelled or deemed unfit for public school but the state (city?) still had a responsibility to educate them. Given the alternatives our kids were lucky I guess. I heard some unimaginable horror stories (from the kids) about the juvenile detention facilities in Baltimore.
On a side note: I also grew up in poverty (divorced parents, educated single-mother in the 1970s could not get a decent paying job and "dad" never paid support). But it was first world poverty. We didn't have a car. But I never went to bed hungry and we always had heat & electricity. Naive me at first thought I could somehow related to these kids. I learned quickly that is like thinking you know what it's like to be blind because you wore an eye patch for Halloween. Another story that has never left me was the time we took an 8 year old boy for a home visit with his grandmother in Boston. I went to college in Boston. I thought I had explored every inch of that city. I learned that day how wrong I was. Row after row of 3 story, grey concrete building. Burned out cars on the side of the road. Traffic lights broken. We get his grandmother's building and the front door is gone. Not broken, gone. It's February. 10 degrees out. We walk up the 2 flights of stairs to her apartment. There was an elevator but the kid warned us it was too dangerous ("sometimes bad men try to jack you"). We get to his grandmother's apartment door, I mean blanket. Her door was gone too. In it's place was a blanket and behind the blanket was a bookcase blocking the door. They move the bookcase and in a room maybe 12' x14' are at least 15 people, mostly kids all watching tv sitting on a mattress on the floor. Our kid disappears in the throng and we hightail it out of there. I've never felt as white as I did then. That was the last day I ever complained about my childhood. I had it great compared to many.